NanoFishNest

Pygmy Corydoras Care: Tank Size, Water, Food, Tank Mates & Breeding

Adrian XH — Fri, 09 Oct 2026 16:47:43 +0000

Pygmy corydoras grow to only about 2 to 3 cm, yet they are not a fish for any small tank. They live in shoals, swim in open midwater as well as on the bottom, and gulp air at the surface. Keep at least 6, preferably 10 or more, at 22 to 26 °C in a mature tank with a footprint of 45 x 30 cm or larger. Feed foods small enough for a 2 cm fish, and choose tank mates too small to eat them.

This guide covers Gastrodermus pygmaeus, still sold as Corydoras pygmaeus. Each figure traces to published research, veterinary guidance, specialist breeders, or Derek Lambourne’s 1995 handbook Corydoras Catfish.

Pygmy corydoras care: quick facts

Fact	Figure
Scientific name	Gastrodermus pygmaeus (Knaack, 1966), formerly Corydoras pygmaeus
Adult size	Males about 2 cm, females up to about 2.5 to 3 cm (standard length)
Native range	Amazon basin in Brazil, Colombia, Ecuador and Peru
Group size	6 minimum, 10 or more preferred
Tank footprint	45 x 30 cm minimum, 60 to 76 cm long for 10 or more
Temperature	22 to 26 °C (72 to 79 °F)
pH	About 6.4 to 7.4, kept stable
Hardness	Soft to moderately hard, about 2 to 12 °dGH
Diet	Baby brine shrimp, microworms, fine flake, small frozen foods
Breeding	Eggs placed on surfaces, hatching in 3 to 4 days
Lifespan	Not documented

How firm are these numbers

No study sets a minimum tank, group size or ideal temperature for this species. Those figures are specialist consensus. Water-quality limits come from veterinary guidance for freshwater fish. Air-breathing and diet data come mostly from the bronze cory, Corydoras aeneus, and are marked as such.

Pygmy corydoras tank size and footprint

Every tank figure for G. pygmaeus is husbandry guidance, since no study sets a minimum. Seriously Fish gives a base of 45 x 30 cm, about 41 L, and says a large group fits a 45 x 30 x 30 cm tank. Breeder Mike Hellweg writes that the miniature corys shine in a 76 L (20-gallon) long tank or larger. For 10 or more fish, a tank 60 to 76 cm long is the safer choice.

Footprint matters more than height. The shoal needs open water to swim in, open floor to forage on, and a short trip to the surface for air. In the bronze cory, water depth between 10 and 120 cm changed air-breathing rates. The pattern depended on oxygen level and activity. Height is not neutral for an air-breather, but no study shows a harmful height.

Small volumes swing in temperature and ammonia faster. Stock only a cycled tank that reads 0 ammonia and 0 nitrite. The stock calculator helps when the corys share the tank.

How many pygmy corydoras to keep together

Keep at least 6, and preferably 10 or more. Seriously Fish, ScotCat and Hellweg agree on that floor. Hellweg describes pygmies forming tight groups of up to several dozen as they forage. No experiment has tested group size in this species, so 6 is a consensus figure.

Lambourne wrote that it “likes to swim in a shoal and is one of the few Corydoras species that likes to swim in mid-water.” Research describes the related bronze cory as highly gregarious, with fish communicating through touch.

Buy several young fish at once. Lambourne advised that over one or two adults, which also makes a breeding pair likely. Females grow larger and fuller than males, a difference best seen from above.

Water parameters: temperature, pH and hardness

Parameter	Target	Basis
Temperature	22 to 26 °C, 22 to 25 °C long term	Species profiles and breeders; no thermal study
pH	6.4 to 7.4	Species profiles; stability first
GH	About 2 to 12 °dGH	Avoid near-zero mineral water
KH	Low but not zero, about 2 to 3 °dKH	Lab practice; prevents pH crashes
Ammonia and nitrite	0	Un-ionized ammonia below 0.05 mg/L
Nitrate	Below 20 mg/L	40 mg/L was the lab ceiling
Oxygen	Above 5 mg/L	Surface kept open for air gulps

Four species profiles agree on 22 to 26 °C. Hellweg keeps the miniature corys at 22 to 25 °C and warns only against water that gets too warm. Lambourne warned that many aquariums run at 25 to 27 °C, too warm. No thermal study exists for G. pygmaeus.

A pH of 6.4 to 7.4 in soft to moderately hard water covers most successful keeping. FishBase lists pH 6.0 to 8.0 and 2 to 25 °dH, but those figures come from a 1996 hobby atlas. No published water chemistry from a wild pygmy cory site turned up in this research. Lambourne’s records show related dwarf species spawning in aged tap water at pH 7.3 to 7.4 and 12 to 14 °GH. Captive-bred fish do not need acidic, mineral-free water. Veterinary tables flag total hardness below 20 mg/L, about 1 °dGH, as a lack of minerals.

Water with almost no alkalinity lets pH crash, and nitrifying bacteria stop working below pH 6. A Corydoras research lab settled on remineralized RO water at GH 4 to 5 °dGH and KH 2 to 3 °dKH.

pH also sets how toxic ammonia is. At 26 °C, 0.60% of total ammonia is in the toxic un-ionized form at pH 7.0. At pH 8.0 the share is 5.74%, so the same test reading is about ten times more dangerous. Tissue damage begins above 0.05 mg/L of un-ionized ammonia. Kits that report nitrate-nitrogen (NO3-N) need the reading multiplied by 4.4 to give nitrate.

Change 30 to 50% of the water weekly, matched for temperature and chemistry. Hellweg changes 50% or more weekly, and the lab held nitrate below 40 ppm with 40 to 50%. Use a conditioner rated for chloramine. Lambourne’s advice to let tap water stand 48 hours works for chlorine, but standing water is not a safe way to remove chloramine.

Tank setup: substrate, plants, filtration and flow

Use a fine, smooth, rounded substrate and keep it clean. No controlled study links substrate type to barbel damage in any Corydoras. Lambourne recommended small pea gravel and warned only against grains too large or too sharp. Heiko Bleher favors sand for most Corydoras, yet calls a fine substrate “not essential” for pygmaeus and hastatus. Seriously Fish links barbel infections to dirty or unfavorable conditions, which makes hygiene the variable that matters most.

One old record cuts against the sand rule. Breeding the dainty cory (C. habrosus), Lambourne found that fine sand “caused considerable damage to the barbels of the fry,” while adults were unaffected. He switched to 1.5 mm gravel. Seriously Fish reports pygmy cory fry less prone to disease over a thin layer of sand. Grain shape and cleanliness decide the outcome more than the label.

Plant heavily, but leave open water and an open strip at the front for feeding. Lambourne noted the species “seems to be happiest in a well-planted aquarium.” Floating plants give shade but must not seal the surface. In very low oxygen, bronze corys survived only if they could reach the surface.

A mature sponge filter suits the species, and breeders use them. Hellweg reports that all three miniature corys appreciate a decent current, and that sponge, canister and waterfall filters all work. Cover any filter intake with a sponge, since adults measure about 2 cm and new fry a few millimeters. The sponge filter guide covers sizing.

Lighting is not critical. Seriously Fish says the species prefers dim light, while Hellweg finds the miniature corys out in the open all day, so provide shade. Fit a lid, as Lambourne recommends. Use a guarded heater and check a separate thermometer daily.

What pygmy corydoras eat and how to feed them

No gut-content study exists for this species. Chironomid larvae, then nematodes, were the main prey of wild C. paleatus at the healthier reaches of a prairie stream. Juvenile bronze corys of 25 to 30 mm ate up to 75,849 nematodes each in 24 hours in a lab trial.

A peer-reviewed husbandry protocol names frozen baby brine shrimp and live microworms as foods that work for C. pygmaeus. Add newly hatched brine shrimp, crushed flake, fine sinking granules, small frozen Cyclops and Daphnia, and sifted live Daphnia. A microworm culture and a Daphnia culture supply live food cheaply.

Feed small amounts once or twice a day, more often when conditioning for breeding. Lambourne fed 2 to 3 small meals a day, each eaten within 2 to 3 minutes.

Corydoras appear to find food mainly by smell and eat more slowly than midwater and surface feeders. Faster tank mates can strip a meal before the corys reach it. Drop some food where the shoal forages, or feed after the other fish are full. Bellies should look slightly rounded, never pinched. Leftovers are not a diet, since uneaten food rots and fouls the water.

Tank mates for pygmy corydoras

Category	Examples	Reason
Suitable	Small rasboras such as Boraras, small danios, pencilfish, hatchetfish, small peaceful tetras	Similar size, peaceful
Caution	Dwarf shrimp, fast-feeding small fish	Shrimplets are plausible prey; fast fish win the food
Avoid	Angelfish, gouramis, larger catfish, three-spot or Paraguay tetras, any fish that can swallow a 2 cm fish	Predation or harassment

Seriously Fish warns that angelfish, gouramis and larger catfish will find it “an ideal snack.” It is easily intimidated by larger tank mates and loses out to them at feeding time. Hellweg advises against three-spot or Paraguay tetras. Chili rasboras and ember tetras fall in the small, peaceful size range the sources recommend.

Adult dwarf shrimp are commonly kept with pygmy corys. Nobody has tested whether the corys eat shrimplets, though Corydoras do eat small crustaceans.

Normal behavior, stress signs and health

Midwater swimming is normal

Pygmy corys forage near the bottom and swim in midwater in short bursts, often as a tight group. The habit is less pronounced than in the dwarf cory, G. hastatus, which spends most of its time in midwater. At night they rest in small groups on the bottom.

Air gulps and winking

Brief dashes to the surface are normal, since Corydoras breathe air through the gut. In the bronze cory the mouth is exposed for only 0.06 to 0.07 seconds per breath, and the air leaves through the vent. Breathing occurs at every oxygen level, from 1 to 45 times an hour. Gulping that rises across the whole group is a warning. Severe hypoxia raised group breathing by about 45% in one study. Continual dashing, Lambourne wrote, means testing the water.

The eye rolling called winking is normal too. The eyes move independently and rotate in their sockets. Lambourne suggested it cleans them, and no study has tested that.

Signs of stress or illness

The whole group gulping at the surface more than usual
A scattered shoal, or fish hiding all day
Frantic darting or rubbing against decor
Clamped fins, lethargy or a pinched belly
Red, shortened or missing barbels
White spots or cloudy eyes

Behavior alone does not diagnose disease. Test ammonia, nitrite, nitrate and temperature first. Lambourne found a water change usually fixed the problem.

Quarantine, medication and when to call a vet

Quarantine new fish for 30 to 60 days, the veterinary standard. Restart the clock if another fish joins. Lambourne’s 10 to 14 days falls short of that. In one Amazon survey, 66% of 151 wild Corydoras carried parasites, mostly internal.

The old rule of half-dosing medication for scaleless fish has never been tested. Corydoras are covered in bony plates. One Corydoras species ranked among the most copper-tolerant of nine Amazonian fish in a lethality test, which does not make treatment doses safe. Copper risk depends on alkalinity. Below 50 ppm, about 2.8 °dKH, UF/IFAS advises against copper treatment, and water at the lab’s KH of 2 to 3 °dKH sits at or below that line. Remove activated carbon while medicating, since it absorbs the drug. Losses in good water, or infections needing antibiotics, call for an aquatic vet. The American Association of Fish Veterinarians runs a Find a Fish Vet search.

The Corydoras family has venom glands at the fin spines. In one injection test, spine extract from C. paleatus caused nothing beyond color loss in bass. Claims that stressed corys poison tank mates in transport bags have never been tested. Net gently, since the dorsal and pectoral spines lock rigidly outward.

Breeding pygmy corydoras

Hellweg calls the species easy to induce to spawn. Lambourne recorded that “usually no temperature reduction is needed to induce spawning.” Many larger Corydoras spawn after a cold water change. In a research colony, heavier feeding and twice-weekly water changes were associated with spawning.

Pairs form the T-position on a surface. The female places her eggs singly or in small clusters on glass, plants or the filter. Reported egg sizes run from 1 to 2 mm, and eggs hatch in 3 to 4 days. Lambourne noted that the female’s eyes dilate during spawning. For the related dwarf cory he treats their return to normal as the signal to remove the adults.

Well-fed adults rarely eat eggs or fry. Hellweg leaves them together for about 3 weeks, which yields several dozen to several hundred fry. In a lab colony, 20 to 50% of Corydoras eggs were infertile and turned milky white within a day. Remove white eggs before fungus spreads. Start fry on microworms, then newly hatched brine shrimp and powdered flake. Fry of this species are harder to rear than those of larger Corydoras. Adult coloring appears at about 6 weeks. The full method is in the pygmy corydoras breeding guide.

Pygmy cory, dwarf cory or habrosus: telling them apart

Three tiny corys share the shop tank, and labels mix them up. Since 2024 the pygmy cory has been Gastrodermus pygmaeus, and the 2024 analysis pairs it with the dwarf cory, G. hastatus. The dainty cory, formerly C. habrosus, is now Hoplisoma habrosum, in a different genus.

Feature	G. pygmaeus	G. hastatus	H. habrosum
Flank pattern	Thick black stripe ending in a tail-base blotch	Thin, diffuse stripe and a diamond spot at the tail base	2 to 3 blotches on a speckled body, no continuous stripe
Swimming level	Midwater and bottom	Mostly midwater	Nearer the bottom
Native range	Amazon basin	Amazon and Paraguay basins	Orinoco basin
IUCN status	Least Concern	Least Concern	Near Threatened

Boxes labeled hastatus often hold pygmaeus, as Hellweg found several times. The range is also wider than many sites claim. The type locality lies on the Rio Madeira in Brazil, but the Catalog of Fishes lists the Amazon basin in Brazil, Colombia, Ecuador and Peru.

No lifespan has been documented for G. pygmaeus. The 3 to 5 years quoted by shops has no traceable source.

Pygmy corydoras myths checked

Claim	Verdict	Evidence
They need sand	Not proven	No study; smooth fine gravel also works
Air-breathing makes them tolerant of dirty water	Partly false	Air adds oxygen but does not shield the gills from ammonia or nitrite
A cold water change is needed to spawn	Usually false	Lambourne: usually not needed
Stressed corys poison tank mates	Untested	Gland exists, effect never measured

Pygmy corydoras FAQ

How many pygmy corydoras should be kept together?

At least 6, and preferably 10 or more. That floor is specialist consensus, since no experiment has tested group size.

What size tank do pygmy corydoras need?

A footprint of at least 45 x 30 cm, about 41 L, for a small group, and 60 to 76 cm of length for 10 or more. Footprint matters more than height.

Can pygmy corydoras live in a 10 gallon tank?

A standard 10-gallon tank (about 38 L, 51 x 25 cm) sits just under the common 45 x 30 cm guideline. A research lab considers it acceptable for small Corydoras, but a 20-gallon long gives a group of 10 more room. A 5-gallon tank falls below every adult-keeping guideline in the sources.

Do pygmy corydoras need sand?

No study proves it. A fine, smooth, rounded substrate kept clean is the safe choice, and small pea gravel also works.

Why do pygmy corydoras swim to the surface?

They breathe air through the gut, so brief dashes are normal. Gulping that rises across the whole group signals low oxygen or poor water.

What do pygmy corydoras eat?

Foods small enough for a 2 cm fish: baby brine shrimp, microworms, crushed flake, fine granules and small frozen foods. Place some food where the shoal forages, since faster fish eat first.

Can pygmy corydoras live with shrimp?

Adult dwarf shrimp are commonly kept with them. Whether the corys eat shrimplets has never been tested. Corydoras eat small crustaceans, so some shrimplet losses are possible.

How long do pygmy corydoras live?

No lifespan has been documented for this species. The 3 to 5 years quoted by shops has no traceable source.

Sources

Lambourne, D. (1995). Corydoras Catfish: An Aquarist’s Handbook. Blandford.
Tencatt, L.F.C. and Pavanelli, C.S. (2015). Neotropical Ichthyology 13(2): 287–296.
Dias, A.C. et al. (2024). Zoological Journal of the Linnean Society 203(3): zlae053.
Eschmeyer’s Catalog of Fishes, genus Gastrodermus, accessed October 2026.
Chiang, A. et al. (2024). Husbandry protocol for Corydoras catfish. JAALAS 63(5): 472–479.
Kramer, D.L. and McClure, M. (1980). Canadian Journal of Zoology 58: 1984–1991.
Pineda, M. et al. (2020). Journal of Experimental Biology 223: jeb222133.
Bertora, A. et al. (2021). Anais da Academia Brasileira de Ciências 93(3): e20200981.
Majdi, N. et al. (2018). Annales de Limnologie 54: 29.
Wright, J.J. (2009). BMC Evolutionary Biology 9: 282.
Duarte, R.M. et al. (2024). Environmental Pollution 341: 122988.
Ferreira, D.O. et al. (2019). Anais da Academia Brasileira de Ciências 91(1).
Tampa Bay Water: monochloramine information for fish owners.
Merck Veterinary Manual and UF/IFAS (FA031, FA-13) water-quality guidance.
Hellweg, M. Corydoras in Miniature. Tropical Fish Hobbyist.
Seriously Fish, PlanetCatfish, ScotCat and FishBase profiles; Bleher, H. (2009), Practical Fishkeeping.

Aquarium Fish Stock Calculator: How Many Fish Fit in Your Nano Tank

Adrian XH — Wed, 07 Oct 2026 10:45:39 +0000

This free aquarium fish stock calculator checks your nano tank plan. It checks adult size and swimming space, plus school size and water range. No signup.

For species profiles and group sizes, see the nano fish guide.

It won’t give you a maximum fish count. Nobody can work that out from a form. It shows you which requirement your plan fails, and where the advice comes from.

The nano tank planner

Aquarium Fish Stock Calculator

Plan the fish that fit your tank—and their needs. This aquarium fish stock calculator checks adult size, swimming space, social groups and water conditions before you build your stocking list.

Free · no signupNano-focused freshwater checksSources reviewed 5 October 2026

Your aquarium

Rectangular freshwater tanks only. Enter internal dimensions to the waterline. Presets are illustrative dimensions, not measurements of your aquarium.

Best Aquarium Heaters: Picks by Tank Size (2026)

Adrian XH — Tue, 06 Oct 2026 08:27:48 +0000

For most tanks get an EHEIM Jäger and size it to your room temperature as well as your gallons. Over about 40 gallons you should run two smaller heaters. Put both on a controller and switch its high-temperature cutoff on. The controller BRS calls the most popular ships with that cutoff set to 212 °F, the temperature water boils at.

Jump to: See the picks · Heater size chart · Wattage calculator · Stop a heater from cooking your tank · FAQ

Best aquarium heaters: quick picks

Best overall

EHEIM Jäger (thermocontrol)

Glass heater with a recalibration ring. Nine sizes from 25 to 300 watts.

You can correct the dial when it reads off.
Shuts itself off if it runs dry.
3-year warranty that excludes glass damage.

Check first: EHEIM says vertical mounting only, no deeper than 0.5 m.

Check Jäger prices on Amazon

Choose your wattage from the size table first.

Best for nano tanks and bettas

Fluval P10, P25 and P50

Preset polymer heater. No glass and no dial to bump.

P10 covers up to 3 gallons. P25 covers up to 6.
Holds 76 to 78 °F.
2-year warranty with proof of purchase.

Check first: You can’t change the temperature.

See Fluval P on Amazon

P10 is for up to 3 gallons, P25 for up to 6 and P50 for up to 15.

Best shatterproof heater

Aqueon Pro

Metal core under thermal plastic. No glass parts.

Sizes from 50 to 300 watts.
Adjustable from 68 to 88 °F.
Limited lifetime warranty with a dated receipt.

Check first: It tops out at 88 °F.

See the Aqueon Pro on Amazon

Size it from the table above, not the gallon rating on the box.

Best for 55 to 75 gallons

Two Jägers plus an Inkbird ITC-306A

Two half-size heaters on one controller with its alarms set.

If one heater dies, the other keeps the tank warm.
If one sticks on, the tank warms slowly.
The controller cuts power at your high limit.

Check first: Set the controller’s high alarm. It ships at 212 °F.

See the Inkbird ITC-306A on Amazon

One controller runs two heaters. Set the high alarm on day one.

Situation	Pick	Sizes	Why
Best overall	EHEIM Jäger	25 to 300 W	Recalibration ring, dry-run shutoff, 3-year warranty
Nano tanks and bettas	Fluval P	10, 25, 50 W	No glass. Sized for small water volumes.
20 to 40 gallons	EHEIM Jäger 75 or 100 W	75 to 100 W	EHEIM rates 75 W for 15.8 to 26.4 gal and 100 W for 26.4 to 39.6 gal
55 to 75 gallons	Two Jägers + Inkbird ITC-306A	2 × 100 W or 2 × 150 W	Backup heat, slower runaway, alarms
Shatterproof	Aqueon Pro	50 to 300 W	No glass parts. Tilt, overheat and dry-run shutoffs.
Titanium	BRS Titanium Heater System – WiFi	100 to 600 W	Titanium element on an Inkbird controller
Saltwater and reef	Innovative Marine Helio PTC	100 to 700 W	Detects a heater or sensor out of water. Dual-element options.
Canister filter owners	Hydor ETH inline	200 or 300 W	Nothing inside the tank

All picks at a glance.

What size aquarium heater do you need?

Size the heater to the gap between your coldest room temperature and your target water temperature. Gallons are only half the answer. For a typical 10 °F gap you need about 50 watts for a 10-gallon tank. You need 75 to 100 watts for 20 gallons and 150 watts for 55. A 75-gallon tank needs about 200 watts.

A heater doesn’t heat gallons. It replaces the heat your tank loses to the room. A tank in a 75 °F room barely loses anything at 78 °F. The same tank in a 63 °F basement loses heat all day. So measure your room on its coldest night first.

Tank	+5 °F	+10 °F	+15 °F	+20 °F (extrapolated)
5 gal	15 W	25 to 50 W	50 W	75 W
10 gal	25 W	50 W	75 W	100 W
20 gal	50 W	75 W	125 W (pair: 2 × 75 W)	150 W (pair: 2 × 75 W)
30 gal	50 W	100 W	150 W (pair: 2 × 75 W)	200 W (pair: 2 × 100 W)
40 gal	75 W	125 W (pair: 2 × 75 W)	200 W (pair: 2 × 100 W)	250 W (pair: 2 × 125 W)
55 gal	75 W	150 W (pair: 2 × 75 W)	250 W (pair: 2 × 125 W)	300 W (pair: 2 × 150 W)
75 gal	100 W	200 W (pair: 2 × 100 W)	300 W (pair: 2 × 150 W)	400 W (pair: 2 × 200 W)
100 gal	125 W	250 W (pair: 2 × 125 W)	400 W (pair: 2 × 200 W)	500 W (pair: 2 × 250 W)

Heater watts by tank size and temperature rise (room to target). Pair = two heaters of that size.

How we built this table

Filterless Nano Aquarium: Rules, Limits & Failures

Adrian XH — Mon, 05 Oct 2026 15:46:00 +0000

Yes, a filterless nano aquarium can work. It works when the tank is shallow, heavily planted, lightly stocked and mature. Shrimp and snails are the safe bet. Fish are harder, and in some places illegal. Plants do the filtering, so if the plants stall, the tank fails.

For species that suit small tanks, see the nano fish guide.

Check your setup against the rules below before you spend a cent on animals. A wrong call costs you the whole tank. If a “self-sustaining tank” video brought you here, this guide covers the limits and failures to check before you copy it.

The thresholds in this guide are conservative editorial guidance built from published research. They don’t come from a long build log. Every claim is sourced at the bottom, and where the evidence is thin, the text says so.

What “filterless” actually means

A filterless aquarium has no powered filter. Biological filtration still happens, because bacteria live on every wet surface and plants pull ammonia out of the water.

A filter is a convenient box for those bacteria. The bacteria don’t need the box. They need surface, oxygen and time.

Setup	Powered filter	What it relies on
Filterless / no-tech	No	Plants, surfaces, gas exchange, light stocking
Filterless with a bubbler	No	Same, plus an oxygen safety margin
Low-tech planted	Optional	Plants, modest light, no CO2 injection. May have a filter and heater.
Walstad-style	Optional	A soil layer under a cap, plus heavy planting

Walstad, filterless and natural are not the same thing. Diana Walstad wrote the best-known book on this. She still ran filters in her large deep tanks. In her words: “My point is not to advocate dispensing with filters altogether, but I would urge readers to believe in their plants more than trickle filters.”

Self-sustaining is not maintenance-free

You still feed, trim, top off, test and change water. You do these less often once the tank matures. You never stop doing them.

Filterless is not flowless

Still water isn’t ideal for plants. One plant Walstad cites photosynthesized more at 1 cm per second of flow, and 13 to 29% less at 4 cm per second. Another grew best at 11 cm per second and worse in near-still water.

A single-bubble air pump or a tiny pump on low gives gentle movement. Walstad’s heated 2-gallon tanks used one bubble at a time “to provide gentle water circulation without driving off precious CO2”. That tank is still filterless, because an airstone isn’t a filter.

How do filterless aquariums work?

Four things do the work.

Plants take up ammonium directly. Walstad’s argument is that aquatic plants prefer ammonium over nitrate, and that this makes nitrifying bacteria less critical in a planted tank. A duckweed study backs the preference. All six species tested used nitrate only after ammonium ran out.
Bacteria live on surfaces. Leaves, roots, sand, wood and glass all carry biofilm. Researchers now find that comammox Nitrospira, not the archaea older guides name, dominates most surveyed aquarium filters (30 of 38 in one 2024 survey).
Gas exchange happens at the surface. Oxygen comes in through the top of the water. That’s why shape matters, and it’s the next thing to check.
The bioload stays tiny. Less food in means less waste to process.

Plants and bacteria compete for the same ammonium. Walstad’s practical test: “If nitrates accumulate, it suggests that plant growth is insufficient to remove the tank’s ammonia.”

So your nitrate test is a plant-growth gauge. Nitrate climbing means the plants are falling behind, and bacteria are handling the overflow. Bacteria are the backup. Plants are the system.

That has a flip side. If plants do most of the work, the bacterial backup may be small. A sudden plant crash (melt, heat wave, a hard trim) can leave nothing to absorb the ammonia. This is a reasoned inference, and nobody has measured it in aquariums. Test ammonia after any big plant loss.

What the research hasn’t done is test any of this in a truly filterless home tank over months. Nearly every nitrification study on aquariums used filtered tanks. The one unfiltered study (2 L betta tanks, 25 days) found plants reduced ammonia but didn’t stop it rising. Plants help, but you still need a test kit on day one.

Next up is the one design choice that decides how much oxygen your tank gets.

Shallow vs cube: why shape beats gallons

Oxygen enters through the surface. In a straight-sided tank, surface area per litre equals one divided by the depth. Volume cancels out.

A 15 cm deep tank gives every litre twice the air contact of a 30 cm deep tank. The RSPCA says it directly: “wide tanks are better than tall tanks as they have a larger surface area for the water volume.” Walstad cites “their shallow depth” as a reason her 2026 expo tanks needed no filters or aerators. A betta welfare study speculated that tanks wider than they are deep are likely more suitable.

Here’s the same 20 litres in five shapes:

Shape (20 L)	Water depth	Surface	cm² per litre
Tall column, 20 × 20 cm	50 cm	400 cm²	20
Cube	27 cm	737 cm²	37
Rimless, 30 × 30 cm	22 cm	900 cm²	45
40 × 25 cm	20 cm	1,000 cm²	50
Tray, 50 × 26.7 cm	15 cm	1,334 cm²	67

(These are our calculations from the tank dimensions.)

Recovery time matters too. In still, low-wind conditions, oxygen transfer across the surface levels off around 1 to 2 cm per hour. That means an oxygen deficit recovers on a timescale of roughly depth divided by that speed. It’s about 7 to 15 hours at 15 cm, and 15 to 30 hours at 30 cm. This is a calculation, and nobody has measured it in a tank. Walstad also says to avoid tanks taller than about 18 inches (46 cm) unless they get window light.

Can your tank run filterless? Go / Caution / No

Score your tank with this table. The water-quality values are sourced. The shape, age and stocking thresholds are our conservative editorial guidance. Where a value comes from welfare or retail standards for filtered tanks, treat it as a ceiling to stay under.

Check	Go	Caution	No
Water depth	Shallow and wide	25 to 46 cm	Over 46 cm without window light
Plant coverage	Dense, growing, with a fast grower	Sparse or newly planted	Plants melting or stalled
Stocking	Shrimp and snails only	A few small fish in 30 L+	Fish in a tank under 20 L
Tank age	Over 2 to 3 months, stable	6 to 8 weeks	Under 4 weeks
Dissolved oxygen	6 mg/L or more	5 to 6 mg/L	Under 5 mg/L
Total ammonia	Undetectable	Detectable, fish stable	Rising, or animals stressed
Nitrite	0	Any detectable	0.2 mg/L or more
Nitrate	Under 20 mg/L (check the unit)	20 to 50 above tap	Over 50 above tap
Alkalinity (KH)	Above 100 mg/L CaCO3 (about 5.6 dKH)	50 mg/L or less (about 2.8 dKH)	Under 20 mg/L (about 1.1 dKH)
Room temperature	Stable, matches your species	Summer swings	Heat waves with no plan
Lid	Fitted	Partial	Open top, no mosquito control

Sources for these values: the Merck Veterinary Manual water quality table, UK Defra seller standards (dissolved oxygen at least 6 mg/L, nitrite 0.2 mg/L maximum), and University of Florida extension guidance on alkalinity. The “No” for alkalinity comes from the line that below 20 mg/L, nitrifying bacteria “do not function effectively.”

Nitrate units. Most test kits read nitrate as nitrogen. To get actual nitrate, multiply by 4.4. A reading of “20” can mean 20 or 88 mg/L.

Ammonia and pH. “In most home aquariums, a TAN reading of 1.0 is not a huge concern unless pH exceeds 8.5.” Toxic ammonia depends on pH and temperature, so judge any reading against your pH.

Filterless nano aquarium setup

Passed the table? Then do these in order.

Pick the tank. Shallow and wide. The more water, the easier it is. Our safest beginner recipe is 30 to 40 L, not 5.
Choose a substrate. Inert sand or small gravel is the easy route. A soil underlayer is the classic Walstad method. If you go with soil, keep it to about 1 inch (2.5 cm), unfertilized, under a thin cap. Walstad’s limit for a sand cap is about 0.5 to 0.75 inch (1.3 to 1.9 cm). Sand can seal soil and “suffocate” it. Don’t add fertilizer to soil. Sulfates feed hydrogen sulfide. Nitrate fertilizer gave her 1 to 2 ppm nitrite within a week.
Plant heavily on day one. Include at least one fast grower, such as stems, hornwort or a floater. Slow plants (Anubias, Java fern, moss) give you structure and surface. They don’t process much nitrogen.
Fill with conditioned water. Find out if your utility uses chloramine. See the water section below.
Set your light. This one is disputed. See the next section.
Wait, test, then add animals. Don’t count days.

The light schedule: two camps

The common aquascaping advice is to start at about 6 hours a day and work up to 7 or 8. Walstad says the opposite. She wants at least 12 hours, run as a “siesta” schedule. Lights go on 7 AM to noon, off noon to 4 PM, and on again 4 to 9 PM. Her 2023 article lists “7-hour photoperiods” among the causes of problems. In floating-plant tanks she runs 13 hours or more with no siesta.

Nobody has run a controlled aquarium trial comparing the two. In a filterless tank, plant growth is your filtration, and a short day limits that. Algae is better managed with light intensity and plant mass than by a short day. Start with a siesta schedule, watch the plants, and adjust.

How to cycle a filterless aquarium

It isn’t a normal cycle. You aren’t waiting for a filter to ripen. You’re waiting for plants and surface bacteria to handle the food you’ll add.

Weeks 0 to 3: Expect plant melt and cloudiness. With fresh soil, expect a burst of ammonia. Soil bacteria also pull oxygen out of the water. Walstad’s advice for new soil bowls was to wait a couple of weeks before shrimp, “closely monitor ammonia levels, prepare for water changes and possibly add aeration.” In her 2023 bowls she changed about 80% of the water almost daily for 1 to 2 weeks. She blamed overly fertile potting soil.
Weeks 3 to 8: Test ammonia and nitrite. In filtered home tanks, they cleared by week 3 in two tanks and week 8 in the third. In another study (filtered, 20 to 22 °C), nitrite peaked on days 44 to 58. Your tank may differ. Calendar age doesn’t prove anything.
Add animals when new plant growth is vigorous, ammonia and nitrite are undetectable, nothing smells bad, and a small dose of food doesn’t cause a spike.

Walstad’s book says soil tanks can take fish within days. Her own recent experience says wait. Follow the conservative path. Plant first, wait six to eight weeks, and test.

Don’t lean on bottled bacteria. In a 14-day test, four of five products failed to reduce ammonia, with one tank per product. The authors said the products “should not be recommended as a sole method.” Live plants may be the better seed. In a 2025 study of three filtered home tanks, the two that cleared fastest had live plants. The slowest had artificial plants and the only bottled product. That’s three tanks, so treat it as a hypothesis.

Best livestock for a filterless nano tank

Start with the volume rule. A fish fitting in a tank says nothing about whether the tank is right for it.

Tank	What fits (editorial guidance)
2 to 5 L	Plants, microfauna, a few small snails. No fish. Shrimp only for experienced keepers.
10 L	A small shrimp colony and snails. Normally no fish.
20 L	One betta in a heated, planted, wide tank, or a shrimp system
30 L	One betta, shrimp, or a conservative school of tiny rasboras in a long tank, once mature
40 L	Around 10 chili rasboras, or a betta or shrimp system. Add gentle aeration.

Animal	Bioload	Verdict
Neocaridina (cherry shrimp)	Low	Candidate. Best fit. Breeding does best near 28 °C and stops at 32 °C.
Ramshorn and bladder snails	Low, but they multiply	Candidate. A population boom means too much food.
Nerite snails	Low	Candidate if there’s enough biofilm. A sterile new tank may starve them.
Malaysian trumpet snails	Low, but they multiply	Caution. Parthenogenetic, so one snail can found a colony.
Betta	Moderate	Candidate at 20 L+, heated and heavily planted. See the welfare section below.
Chili rasbora, ember tetra	Low each, school needed	Candidate at 30 to 40 L long. Stock at the low end.
Medaka	Moderate	Candidate at 40 L+. Cool water.
Endler-type livebearers	Grows fast	Caution. Males only, in 30 to 40 L+.
Caridina (bee shrimp)	Low	Avoid. They need tightly controlled soft water.
Pygmy corydoras (now Gastrodermus pygmaeus)	Moderate	Avoid. Social, active and oxygen-hungry.

Fish sizes quoted from FishBase are maximums. A chili rasbora’s common length is 1.8 cm, but it reaches 3.5 cm.

What the welfare research says about bettas

One study (Oldfield and Murphy, 2024) found that “at least a 10-L aquarium is required to ensure full expression of swimming behaviour.” They tested 0.5 L, 10 L, 38 L and 208 L, and nothing in between. So 10 L is the smallest size shown to be enough. It isn’t a proven minimum.

Another (Clark-Shen and colleagues, 2024) tested 1.5, 3.3, 5.6 and 19.3 L. Fish were more active in the biggest tank and rested and hovered less. They recommend at least 5.6 L for retail display and more at home. The UK trade body OATA recommends 20 L for a single male. We use 20 L as the practical target.

Bettas also tolerate extreme ammonia in lab tests (a 96-hour LC50 of 7.7 mg/L NH3-N). That says nothing about welfare. Don’t use it as an excuse for bad water.

Check the law before you buy

Some animals in the hobby are regulated. The EU’s 2025 update added the giant ramshorn Marisa cornuarietis, the Chinese mystery snail, the weather loach and the yabby to its invasive species list. Listing bans keeping, breeding, sale and exchange. Pet owners who already had animals may keep them to the end of their lives if breeding and escape are impossible. Plants get no such exemption.

Plants matter here too. In the US, Hygrophila polysperma, Limnophila sessiliflora and all four giant salvinias are federal noxious weeds, and moving them between states needs a permit. The EU list includes Salvinia molesta, water lettuce (Pistia stratiotes, from 2 August 2024), Cabomba caroliniana and Elodea nuttallii. Amazon frogbit isn’t on either list. In Queensland, every Cabomba species except C. caroliniana is prohibited. Name species when you shop, not genera, and check your local rules.

The microfauna bonus

Copepods, seed shrimp and detritus worms show up on their own in a mature tank. They’re usually harmless and feed shrimp and small fish.

Daphnia turn visibly red in low oxygen because they make more hemoglobin. New hemoglobin shows up within 18 hours, and it takes up to 11 days to level off. So it’s a slow hint and not a gauge. Warm water also raises it, and a red-pigmented bacterial pathogen infects some Daphnia. Ramshorn snails are red for another reason. Their family is the one group of snails with hemoglobin.

Maintenance: what you still do

Task	How often
Look at animals and plants	Daily
Check dawn breathing	Daily in new tanks, and after any heat wave
Top off with the right water	As needed
Feed small, remove leftovers	Every feeding
Trim plants	Weekly to monthly. Dead plants pollute.
Test ammonia and nitrite	2 to 3 times a week for the first month with animals
Test nitrate, pH and KH	Weekly at first, then monthly
Water changes	See below

Water changes: the conflict, resolved

One guide says 20 to 30% every week. Walstad’s established tanks often “go for six months or more without water changes.” Both are right at different tank ages.

Stage	Approach	Why
Weeks 0 to 3, fresh soil	Test every 2 to 3 days. Change a large volume if ammonia or nitrite shows.	Soil releases nutrients and pulls oxygen.
First 1 to 2 months with animals	20 to 30% weekly	Plants and surface bacteria are still building.
Mature, light stock, plants growing, nitrate near zero	Stretch the gap on data. Go monthly, then up to Walstad’s 3 to 6 months (25 to 50%).	Plants export nitrogen. Humic compounds protect against metals.
Any tank kept only by topping off	Test KH and pH monthly	Alkalinity drops over time.
Old tank with low pH and high ammonia	Small daily changes. Never one big one.	A big change raises pH and converts harmless ammonium into toxic ammonia.

The last row matters most. Merck says an old, acidic tank “should be returned to normal by performing daily small water changes to avoid pH shock and ammonia toxicosis that can occur as the pH increases.” Don’t “fix” a neglected tank with one giant change.

Two tap-water traps

Chloramine. Many utilities use it. A thiosulfate dechlorinator breaks it apart and leaves its ammonia in the water. At the legal maximum of 4.0 mg/L, that can release up to about 0.79 mg/L ammonia nitrogen (our calculation). A 50% change adds up to about 0.4 mg/L. Ask your utility. If it uses chloramine, use a conditioner rated for it, and test the next day.

Metals. Walstad’s well water had 0.8 ppm zinc, and that was enough to kill her shrimp. US tap rules allow 1.3 mg/L copper, and regulators sample water that sat in pipes for at least six hours. A freshwater prawn’s copper LC50 is 0.0313 mg/L. Nobody has published a cherry shrimp copper LC50, so that’s an analogy. Run the tap before you collect water, and use a conditioner that binds heavy metals. Walstad also notes that each water change “is, in essence, a fresh dose of metals” if your tap is contaminated.

Why filterless tanks fail

Failures tend to follow tank age, and each stage has its own trap.

Weeks 0 to 3: Soil releases ammonia and consumes oxygen. Plants melt after transplant. Animals added too early die.
Months 1 to 3: A plant crash exposes a small bacterial reserve. Heat, a hard trim or a light failure can do it.
Month 6 and later: Alkalinity wears down. Nitrification uses about 7.14 mg of alkalinity per 1 mg of ammonia nitrified. In a KH 2 tank, that’s roughly 20% of your buffer for every 1 mg/L (our calculation). Below about pH 6.5, nitrification slows sharply. The pH drops, and the rescue trap above kicks in.
Summer: Warm water holds less oxygen (9.09 mg/L at 20 °C, 7.56 at 30 °C) while animals need more. A fish’s resting oxygen demand rises by more than double for every 10 °C in many species (median Q10 of 2.40). At 32 °C, cherry shrimp females lose their eggs.

Symptom	Likely cause	Fix
Milky, cloudy water	Bacterial bloom from too much food or rot	Feed less, remove rot, add gentle aeration
Rotten-egg smell	Sulfide or decaying matter	Act now. Remove the source, aerate, change water.
Gasping or surface crowding	Low oxygen, or high CO2	Aerate immediately. Test ammonia and nitrite.
Spreading algae	Plants are the problem first	Fix plant growth, then trim light and food
Slimy mats	Dead-flow zones with organic buildup	Siphon, improve flow, reduce organics

Four hidden causes of failure

The afternoon spike. Photosynthesis raises pH during the day. Each unit of pH multiplies the toxic share of ammonia about ten times. At 25 °C, 0.5 mg/L total ammonia is about 0.003 mg/L toxic ammonia at pH 7.0, and about 0.027 mg/L at pH 8.0 (our calculation). Test pH in the morning and again in the late afternoon at least once. In one low-alkalinity reservoir full of plants, daily pH swung 0.88 units on average, and 2 to 3 units at the extremes.
The floating-plant blanket. A full mat blocks the oxygen inlet and shades what’s below. In unfiltered 2 L tanks, Wolffia tanks averaged 3.88 mg/L dissolved oxygen, against 6.16 with no plants. In ponds, those with about 95% duckweed cover had far more oxygen-free sediment. Keep open water. Thin floaters often.
Surface film. A scum can trap plant bubbles under it. Walstad’s fix is to agitate the surface or blot it with newspaper.
Bottom stratification. In a lake plant bed, oxygen hit 177% saturation at the canopy and often hit zero near the sediment in daylight. Nobody has measured this in an aquarium. But a thick stem forest in still water is a candidate.

Light inhibits some nitrifiers in lab cultures. A comammox species stopped nitrifying completely under continuous dim light, and archaea showed no recovery in the dark phases. These were pure cultures and not tanks. But it’s a reason to give nitrifiers dark space, like the substrate, hardscape, root mats and the area under floaters.

Filterless vs sponge filter

	Filterless	Sponge filter
Cost and noise	Cheapest, silent	Cheap, a little noise
Oxygen and flow	Depends on shape and plants	Built-in surface movement
Bacteria surface	Plants, substrate, hardscape	The sponge, plus all of the above
Failure margin	Small	Larger
Official guidance for fish	Against	For

Official guidance mostly says fish tanks need filters. The RSPCA (England and Wales) says: “No fish should be kept in tanks without a well set up and maintained filter.” OATA says a betta needs at least 20 L and “Whatever the size, a filter is always essential.” RSPCA Australia and SPCA New Zealand also call for filtration.

Austria goes further. Its animal-keeping ordinance bans keeping even small fish long-term in tanks under 54 L, lists “Filter, Heizung, Pumpe” as minimum equipment, and requires that ammonia and nitrite be undetectable. It covers vertebrates, so a shrimp-only tank falls outside it. Germany’s 1998 federal guidance also uses 54 L as the minimum for permanent keeping, and it’s being revised. Switzerland sets litres per centimetre of fish in law. The 54 L and filter advice there comes from the federal veterinary office’s guidance page, not the ordinance.

This guide leads with shrimp and snails for that reason. For fish, a hybrid is the better call: an air-driven sponge filter on gentle flow, plus heavy planting. You keep the plant-led system and add a margin.

Gear worth buying

A thermometer. Not optional. Small tanks track the room within hours, so a hot afternoon can cook a nano before you notice.
Test kits. Ammonia, nitrite and nitrate, plus KH and GH. KH shows your buffer eroding before the pH crashes.
A conditioner that handles chloramine and binds heavy metals.
A lid. It cuts evaporation, stops jumpers and blocks mosquitoes. A mosquito egg takes 7 to 10 days to become an adult, and Culex lay rafts of 100 to 300 eggs on standing water. Walstad uses glass lids on all her tanks.
A light on a timer. Plants need a steady schedule.
A small air pump with a single-bubble outlet for fresh soil, heat waves and floater-heavy tanks.
A heater, only if your species need it. Don’t skip one for ideology.

Filterless aquarium FAQ

Can you have a filterless aquarium?

Yes. It works best as a shallow, heavily planted, lightly stocked shrimp or snail tank. It’s harder with fish, and it’s illegal for fish in some places, so check your local rules.

Do nano tanks need a filter?

Not always. But small tanks are less forgiving. Ten milligrams of pollutant is 2 mg/L in 5 L and 0.25 mg/L in 40 L. The bigger the tank, the easier it is.

How long before fish can go in?

Plant first and test. Six to eight weeks is a sensible planning horizon. Readiness means undetectable ammonia and nitrite, strong plant growth and no foul smell. In the studies we found, ammonia and nitrite cleared between weeks 3 and 8 in filtered tanks.

Do you need water changes?

Yes, at first. Do 20 to 30% weekly in the early months. A mature, lightly stocked tank can stretch to monthly, and in Walstad’s case a few months. Let your test results decide.

Can shrimp live without a filter?

Yes. Walstad kept red cherry shrimp in small planted tanks without a filter or heater, as long as they were protected from heavy metals in tap water. But she also found her 1-gallon bowls “were not big enough to maintain a shrimp population.”

Why is my filterless tank cloudy?

Usually a bacterial bloom from extra food or decaying plants. Feed less, remove rot and add gentle aeration. If the water also smells like rotten eggs, treat it as an emergency.

Do I need an air stone?

Not always. Use one for fresh soil, heat waves, dawn gasping and floater-heavy tanks. Floating plants take CO2 from the air, so aeration doesn’t hurt them. In a submerged-plant tank with healthy fish, a single-bubble trickle is plenty.

Can a betta live in a filterless tank?

Bettas have been kept unfiltered in welfare studies and by experienced keepers. But UK, Australian and New Zealand welfare bodies recommend a filter, and Austria requires one. If you try it, use at least 20 L, a heater, dense plants and weekly tests.

Verdict and next step

Try it if you want shrimp or snails, you can fit a shallow wide tank, you’ll plant heavily, and you’ll test for the first two months.

Don’t try it if you want a fish community in a small tank, you’re away for weeks at a time, your room swings in temperature, or you live where filters are required by law.

In a good filterless tank, the plants can process more waste than the animals produce. Keep the margin big. Fewer animals, more plants, more water.

Next step: run your tank through the Go / Caution / No table today. Any “No” means fix that first. Several “Caution” rows mean wait a week and test again. Write down your ammonia, nitrite, nitrate and KH before you add a single animal, so you have a baseline to compare against.

Sources

Walstad is a practitioner source and not a controlled trial. Papers marked abstract-only were read at abstract level.

Walstad DL. Ecology of the Planted Aquarium, 3rd ed. (Echinodorus Publishing, 2012) and 4th ed. preview (2023). Articles at dianawalstad.com: “Potted Plants for Fish Breeding Tanks” (2023), “Small Planted Tanks for Pet Shrimp” (2023), “Nitrogen Uptake by Aquatic Plants” (2017), and blog posts of 29 April 2026 and 8 February 2023.
Xu Y et al. 2026. Effects of aquatic plants on water quality, microbial community, and fish behaviors in newly established betta aquaria. Animals 16(2):247.
McKnight MM, Neufeld JD. 2024. Comammox Nitrospira among dominant ammonia oxidizers within aquarium biofilter microbial communities. Appl Environ Microbiol 90(7):e00104-24.
McKnight MM et al. 2025. Microbial community succession of home aquarium biofilters. ISME Communications 5:ycaf212.
Umbach AK et al. 2026. Fish load impacts biofilter microbial communities (bioRxiv preprint, not peer reviewed).
Scagnelli AM et al. 2023. Efficacy of quick-start nitrifying products in controlled fresh-water aquaria. J Exot Pet Med 44:22-26 (abstract).
Merck Veterinary Manual: water quality reference ranges, Environmental Diseases of Aquatic Animals, and Management of Aquarium Fish.
US EPA. Aquatic Life Ambient Water Quality Criteria for Ammonia, Freshwater (2013).
University of Florida IFAS EDIS FA16, Ammonia in Aquatic Systems.
USGS. Dissolved Oxygen, Techniques and Methods 9-A6.2 (2020).
Oldfield RG, Murphy EK. 2024. Life in a fishbowl. Animal Welfare 33:e1. Clark-Shen N et al. 2024. Life beyond a jar. Animal Welfare 33:e62.
Tropea C et al. 2015, PLoS ONE 10:e0119468 (cherry shrimp and temperature). Baliña S et al. 2018, Biol Bull 234:139 (abstract).
Rabaey JS, Cotner JB. 2022. Pond greenhouse gas emissions controlled by duckweed coverage. Front Environ Sci 10:889289. Wylie GD, Jones JR. 1987, J Freshw Ecol (abstract). Martinsen KT et al. 2022, J Geophys Res Biogeosci 127.
Merbt SN et al. 2012, FEMS Microbiol Lett 327:41-46 (abstract). Gottshall EY et al. 2022, Front Microbiol 13:1022899.
Csontos D et al. 2024. Removal of nitrate and phosphate by aquatic plants during aquarium-based ornamental fish production. N Am J Aquacult 86:413 (abstract).
Kajimura M et al. 2023. Acute toxicity of ammonia and nitrite to Siamese fighting fish. BMC Zool 8:25.
Conway Holroyd S et al. 2026. An ecophysiological approach to improving health outcomes of ornamental shrimp. Conserv Physiol.
RSPCA (England and Wales), “Choosing an aquarium for pet fish”. RSPCA Australia betta guidance (2024). OATA betta care sheet. SPCA New Zealand. Defra retail guidance (2018), Table L-02.
Legal texts: 7 CFR 360.200. Regulation (EU) 1143/2014 with Implementing Regulations 2016/1141, 2017/1263, 2019/1262, 2022/1203 and 2025/1422. Austria 2. Tierhaltungsverordnung, Anlage 5. Switzerland Tierschutzverordnung Annex 2 Table 8. German BMLEH 1998 expert opinion. Queensland Biosecurity (Cabomba).

Best Fish for a 20 Gallon Aquarium: 24 Picks, Stocking Plans and What to Avoid

Adrian XH — Sun, 04 Oct 2026 20:01:25 +0000

The best fish for a 20 gallon aquarium are small, peaceful freshwater species that fill three slots: one school of 8 to 12 tiny fish, one group of 6 to 8 bottom dwellers, and at most one centerpiece. My default is ember tetras with pygmy corys. This guide covers freshwater only. Saltwater and reef need a different plan, and this site does not cover them.

Every fish below has an adult size, a group minimum, a temperature and pH range, a shrimp flag and a bioload rating. Every stocking plan shows the temperature, pH and hardness its fish share. Fish that appear in this guide do not all belong together, so use the plans instead of mixing and matching.

Pick your plan in 30 seconds

These are the beginner fish for a 20 gallon tank that I would buy first, plus 20 gallon fish tank fish ideas for every common situation. Tap a row to jump to the plan.

My first tank, and I want it easyPlan 1: First Tank Classic No heater, cool roomPlan 3: Unheated Room-Temp Planted tank or aquascapePlan 2: Dense Nano One centerpiece fishPlan 6: Betta, or Plan 5 if you are experienced I want shrimp tooPlan 2: Dense Nano (adult shrimp live, expect shrimplet losses)My tap water is hardPlan 4: Livebearer Garden I own a 20 high, not a 20 longPlan 2 or Plan 6, both fit a shorter base

20 gallon long vs high vs hex: why shape changes your picks

Both hold 20 gallons. They do not give fish the same space. A standard 20 long measures 30.25 x 12.5 x 12.75 in (76.8 x 31.8 x 32.4 cm). A 20 high measures 24.25 x 12.5 x 16.75 in (61.6 x 31.8 x 42.5 cm). Those are standard glass sizes. Other brands differ a little, so measure your tank before you shop.

The long has about 25% more floor and a 6 inch longer swim lane. Fish swim and forage along the length, not up the height, so every plan in this guide assumes a long unless it says otherwise.

Top-down view, drawn to scale. Floor area is about 378 sq in for the long and 303 sq in for the high.

Best fish for a 20 gallon long

Best for: every schooling fish here, corys, kuhli loaches, one bristlenose, a betta, a ram pair.

Avoid: nothing in this guide, but fast fish still want more than 30 inches.

Fish for a 20 gallon tall tank

Best for: embers, chilis, CPDs, pygmy corys, a betta, a honey gourami, tall stems.

Avoid: kuhli loaches, bristlenose, rams, and active schools like cherry barbs or X-ray tetras.

20 gallon hex

Best for: the smallest fish only, such as embers or chilis, or a single betta.

Avoid: anything that needs a lane. Hex sizes vary by brand, so measure across the flats.

How many fish can you keep in a 20 gallon?

A 20 long holds one school of 8 to 12 tiny fish, one group of 6 to 8 bottom fish, and at most one small centerpiece. The exact species decide the count. Twelve embers and 12 goldfish are not the same load.

Have a stocking list in mind? Test it in our aquarium fish stock calculator. It covers six nano fish and three invertebrates.

The old one inch per gallon rule counts length and ignores body mass, activity and group size. Even tank manufacturers qualify it by pointing to activity, territory and filtration. Here is the method I would use instead. It is my own editorial guideline, tuned on the plans in this guide, and not a published biological number.

Start with real water. A 20 is 75.7 L on the label. Sand, rock and wood take some of it, so plan on roughly 17 gallons (65 L).
Fill the group minimums first. Never shrink a group to squeeze in another species. Drop the species instead.
Add up adult lengths. Slim fish count 1 per inch. Deep-bodied or heavy-waste fish (bettas, gouramis, rams, bristlenose, barbs) count 1.5. Hyperactive livebearers count 1.25. Snails and shrimp count 0.
Stay under a ceiling of about 30 weighted inches in a 20 long, or about 24 in a 20 high.
Check that nobody collides. A centerpiece claims territory, so give it its own cave, root or plant clump.

Worked example, Plan 1:

Fish	Count	Adult length	Weight	Load
Harlequin rasbora	8	1.8 in	1.0	14.4
Panda cory	6	2.0 in	1.0	12.0
Honey gourami	1	2.2 in	1.5	3.3
Nerite snail	2	1.0 in	0	0.0
Total				29.7 of about 30

That puts Plan 1 right at the ceiling, which is why I call it the fullest plan in the guide. Drop the gourami and you have real margin. Plants help with nitrate and cover, but they do not add swimming room.

Best schooling fish for a 20 gallon tank

These are the small fish for a 20 gallon tank that earn their space. Pick one school for the middle of the tank. Two full schools plus a bottom group overloads the footprint.

Shrimp flag: each card carries one.

Adults and shrimplets are usually left alone.

Risky

Adults are fine and shrimplets get eaten.

The fish can hunt adult shrimp.

Bioload is my editorial rating of waste per fish, not a measured value. Temperature, pH and hardness ranges come from published species profiles.

Schooling

Ember tetra

Hyphessobrycon amandae

The safest first school for a planted 20. Embers stay under 1 inch, ignore each other, and the orange pops against dark soil and green stems. A group of 10 to 12 barely uses any space, which leaves room for a bottom group.

Adult size: 0.8 in (2 cm)
Group size: 10-12 (min 8)
Temperature: 68-82°F (20-28°C)
pH / GH: 5.0-7.0 / 1-10 dGH
Temperament: Peaceful, mid-water
Best shape: Long or high

Shrimp: RiskyBioload: LowDifficulty: Easy

Watch out: Soft to moderate water only. Anything bigger or boisterous will bully them, and 12 embers still eat newborn shrimp.

Ember tetra care guide

Schooling

Neon tetra

Paracheirodon innesi

The classic for a reason. Ten to 12 neons in a 20 long draw a clean blue line through the middle of the tank. They like it cooler than most tropical fish, so run 73-75°F (23-24°C).

Adult size: 1.2 in (3 cm)
Group size: 10-12 (min 8)
Temperature: 70-77°F (21-25°C)
pH / GH: 4.0-7.5 / 1-12 dGH
Temperament: Peaceful, mid-water
Best shape: Long preferred

Shrimp: RiskyBioload: LowDifficulty: Easy-moderate

Watch out: Hard alkaline water and constant 81°F+ heat shorten their lives. Pick fat, fully colored fish at the shop.

Schooling

Harlequin rasbora

Trigonostigma heteromorpha

The easiest school on this list. Harlequins take almost any peaceful tank, eat whatever you drop in, and the copper body with the black triangle looks sharp against plants. 8 to 10 is the number.

Adult size: 1.8 in (4.5 cm)
Group size: 8-10
Temperature: 70-82°F (21-28°C)
pH / GH: 5.0-7.5 / 1-12 dGH
Temperament: Very peaceful, mid-water
Best shape: Long preferred

Shrimp: RiskyBioload: LowDifficulty: Easy

Watch out: They are bigger than embers and neons, so count them as 1.8 inch fish. Keep the school at 8 to 10 if you also want a corydoras group.

Schooling

Lambchop rasbora

Trigonostigma espei

The harlequin’s smaller, calmer cousin. The copper-orange body stands out under dim light and floating plants, and 8 to 12 fit a 20 long with room to spare. It also suits Cryptocoryne, Java fern and dark wood.

Adult size: 1.2 in (3 cm)
Group size: 8-12
Temperature: 73-82°F (23-28°C)
pH / GH: 5.5-7.5 / 1-10 dGH
Temperament: Peaceful, mid-water
Best shape: Long preferred

Shrimp: RiskyBioload: LowDifficulty: Easy

Watch out: Not for hard alkaline water or loud tank mates. Give them floating plants for cover or they hide all day.

Schooling

Cherry barb

Puntius titteya

The one colorful school here that copes with tap water from soft to fairly hard. Males turn deep red. They are calm, they do not nip like tiger barbs, and they suit a planted 20 long with an open lane in the middle.

Adult size: 2 in (5 cm)
Group size: 8-10
Temperature: 68-81°F (20-27°C)
pH / GH: 6.0-8.0 / 2-20 dGH
Temperament: Peaceful, mid to low
Best shape: Long

Shrimp: RiskyBioload: MedDifficulty: Easy

Watch out: They carry more body mass than a tetra, so do not stack a second big school on top. Males display at each other, and a group of 8 to 10 spreads that out.

Schooling

Chili rasbora

Boraras brigittae

The smallest fish in the guide and one of the best for an aquascape. A tight group of 12 to 16 in a mature, shaded, gently filtered tank makes a great show.

Adult size: 0.8 in (2 cm)
Group size: 12-16 (min 8)
Temperature: 68-82°F (20-28°C)
pH / GH: 4.0-7.0 / 1-10 dGH
Temperament: Timid, mid-water
Best shape: Long or high

Shrimp: RiskyBioload: LowDifficulty: Moderate

Watch out: Timid fish that do not belong in a new tank. Add them to a tank that has run for weeks with plants growing. Newborn shrimp are still prey.

Chili rasbora care guide

Schooling

Celestial pearl danio

Celestichthys margaritatus

A species-tank fish in a 20. Current specialist guidance says to keep CPDs in large groups, ideally around 20, because males spar and a big group spreads the aggression across everyone.

Adult size: 0.8 in (2.1 cm)
Group size: 18-20 (as many as you can)
Temperature: 68-79°F (20-26°C)
pH / GH: 6.5-7.5 / 5-15 dGH
Temperament: Shoaling, males spar
Best shape: Long or high

Shrimp: RiskyBioload: LowDifficulty: Moderate

Watch out: Six is the old care-sheet number and it is too low. If you cannot buy 15 or more, pick another fish.

CPD breeding guide

Schooling

White Cloud Mountain minnow

Tanichthys albonubes

The only fish here made for a cool room. Keep 8 to 12 at 61-70°F (16-21°C) with no heater and they stay active and healthy.

Adult size: 1.6 in (4 cm)
Group size: 8-12
Temperature: 57-72°F (14-22°C)
pH / GH: 6.0-8.5 / 5-20 dGH
Temperament: Peaceful, active, upper to mid
Best shape: Long preferred

Shrimp: RiskyBioload: LowDifficulty: Easy

Watch out: Do not pair them with warm-water fish. Past 72°F (22°C) you are outside their listed range.

Best centerpiece fish for a 20 gallon tank

A centerpiece is the fish people look at first. In 20 gallons it needs a spot to claim and tank mates that tolerate it. Most of these five come with caveats, and each card spells them out.

Centerpiece

Honey gourami

Trichogaster chuna

Small, calm and gold. It fits the footprint with room to spare, and a planted tank with floating cover suits it.

Adult size: 2.2 in (5.5 cm)
Group size: 1 to 6 (see note)
Temperature: 72-81°F (22-27°C)
pH / GH: 6.0-7.5 / 2-15 dGH
Temperament: Peaceful, slow, shy
Best shape: Long or high

Shrimp: RiskyBioload: LowDifficulty: Moderate

Watch out: Shops sell it as a single fish. Current specialist guidance says groups of 4 to 6 do best, and other sources say one is fine. I would keep one in a lightly stocked tank, because they lose at feeding time to faster fish.

Centerpiece

Betta

Betta splendens

A 20 gallon is more than most bettas ever get. With floating plants, roots and a slow filter, he behaves like a betta instead of a tenant in a cup.

Adult size: 2.8 in (7 cm)
Group size: 1 male
Temperature: 72-86°F (22-30°C)
pH / GH: 6.0-8.0 / 1-15 dGH
Temperament: Territorial, varies by fish
Best shape: Long or high

Shrimp: NBioload: LowDifficulty: Moderate

Watch out: Specialist guidance recommends one betta per tank. Many bettas hunt shrimp, and a community works only if your fish is calm, so keep a backup tank. Fast, nippy schoolers will wreck his fins.

Centerpiece

Peacock gudgeon

Tateurndina ocellicauda

A small goby with reef-fish color. It stays low to mid-water, takes prepared and frozen foods, and claims a cave or a log.

Adult size: 3 in (7.5 cm)
Group size: 1 to 3
Temperature: 72-79°F (22-26°C)
pH / GH: 6.5-7.5 / 5-10 dGH
Temperament: Colorful, a little territorial
Best shape: Long or high

Shrimp: RiskyBioload: MedDifficulty: Easy-moderate

Watch out: A micropredator. Larger shrimp like Amanos are usually fine, but expect fish fry and Neocaridina shrimplets to vanish.

Centerpiece

Bolivian ram

Mikrogeophagus altispinosus

Active, curious dwarf cichlids that dig and display. One pair with a small school makes a real centerpiece.

Adult size: 3.1 in (8 cm)
Group size: 1 pair
Temperature: 75-82°F (24-28°C)
pH / GH: 6.0-7.5 / 1-10 dGH
Temperament: Peaceful but territorial, shy
Best shape: Long only

Shrimp: RiskyBioload: MedDifficulty: Advanced

Watch out: Specialist guidance lists a 36 x 18 inch base. A 20 long is 30 x 12. This is a borderline fit: one pair, mature tank, sand, and small weekly water changes (10-15%). If you can upsize, do.

Centerpiece

Dwarf gourami

Trichogaster lalius

The brightest centerpiece in this group, at around 3.5 inches.

Adult size: 3.5 in (8.8 cm)
Group size: 1 male or 1 pair
Temperature: 72-81°F (22-27°C)
pH / GH: 6.0-7.5 / 2-18 dGH
Temperament: Shy, males territorial
Best shape: Long or high

Shrimp: RiskyBioload: MedDifficulty: Moderate

Watch out: Dwarf gourami iridovirus is widespread in trade stock, and specialist guidance says stock quality has fallen badly. Buy from a seller who quarantines. Walk away from any dark or lethargic fish. I would pick a honey gourami or a betta first.

Best bottom dwellers and cleanup crew

Corys, loaches and otos have diets and group sizes of their own, so treat them as livestock first. They eat food you put near them and still make waste. Use fine sand for anything with barbels. For a cool tank, swap pandas for salt-and-pepper corys (Hoplisoma habrosum, 1.4 in, 68-79°F). For harder tap water, bronze corys (about 2.75 in, 68-82°F, pH 6.5-7.5, 4-20 dGH) cope better than pandas or pygmies.

Bottom dweller

Panda cory

Hoplisoma panda

The standard 20 long bottom group. Black patches on white, active, and small enough that 6 do not crowd the floor.

Adult size: 2 in (5 cm)
Group size: 6
Temperature: 72-77°F (22-25°C)
pH / GH: 6.0-7.4 / 1-12 dGH
Temperament: Peaceful, bottom
Best shape: Long preferred

Shrimp: YBioload: MedDifficulty: Easy-moderate

Watch out: Fine sand and a clean substrate. Rough gravel wears down their barbels. Feed sinking food directly to them. They are not cleaners.

Bottom dweller

Pygmy cory

Corydoras pygmaeus

Only 1.2 inches, and they spend half their time hovering in midwater. A group of 8 to 12 looks like a school of tiny catfish, and it is the best bottom group for a 20 high.

Adult size: 1.2 in (3 cm)
Group size: 8-12
Temperature: 72-79°F (22-26°C)
pH / GH: 6.4-7.4 / 0-8 dGH
Temperament: Peaceful, bottom and mid-water
Best shape: Long or high

Shrimp: YBioload: LowDifficulty: Easy-moderate

Watch out: Faster fish steal their food. Target-feed crushed sinking pellets or live microworms.

Pygmy cory breeding guide

Bottom dweller

Kuhli loach

Pangio semicincta

The strangest fish in the guide, in a good way. They look like small eels, live in leaf litter and show up at feeding time. Most kuhlis in shops are P. semicincta or close relatives, not true P. kuhlii.

Adult size: 3.9 in (10 cm)
Group size: 5-6 minimum
Temperature: 70-79°F (21-26°C)
pH / GH: 3.5-7.0 / 0-8 dGH
Temperament: Peaceful, shy, bottom
Best shape: Long only

Shrimp: YBioload: LowDifficulty: Moderate

Watch out: They need fine sand, hiding spots, a tight lid and a covered filter intake, because they squeeze through gaps. Keep at least 5.

Bottom dweller

Bristlenose pleco

Ancistrus sp.

The only plecostomus-type catfish I would put in a 20 long. It tops out around 4 to 5 inches, rasps algae and biofilm, and needs driftwood in the tank.

Adult size: 4.5 in (11 cm)
Group size: 1
Temperature: 73-81°F (23-27°C)
pH / GH: 5.5-8.0 / GH flexible
Temperament: Peaceful, territorial with its own kind
Best shape: Long only

Shrimp: YBioload: HighDifficulty: Moderate

Watch out: One fish only. It makes a lot of waste for its size, so keep it out of plans already near the ceiling. Some sources want a 3 foot tank, so treat a 20 long as the bare minimum.

Bottom dweller

Otocinclus

Otocinclus macrospilus and related trade species

Otos graze biofilm and soft algae on plants and glass. In a mature planted 20 with a group of 6, they fit well.

Adult size: 1.4 in (3.5 cm)
Group size: 6+
Temperature: 70-79°F (21-26°C)
pH / GH: 5.5-7.5 / 1-12 dGH
Temperament: Shy grazer
Best shape: Long or high

Shrimp: YBioload: LowDifficulty: Moderate

Watch out: Do not buy them to fix algae in a new tank. New arrivals are often underfed, and a clean tank gives them nothing to eat. Feed algae wafers and blanched zucchini.

Livebearers and shrimp

Livebearers want hard, alkaline water and a single sex. Shrimp want minerals and fish that leave them alone. No fish in this guide is fully shrimp safe, because anything that fits a shrimplet in its mouth will try.

Livebearer

Guppy

Poecilia reticulata

Cheap, bright and easy in hard water. Keep males only and you get color with no fry.

Adult size: 2.4 in (6 cm)
Group size: 5-8, males only
Temperature: 63-82°F (17-28°C)
pH / GH: 7.0-8.5 / 8-30 dGH
Temperament: Peaceful, active
Best shape: Long or high

Shrimp: RiskyBioload: MedDifficulty: Easy

Watch out: Mixed sexes breed nonstop and the tank fills fast. Keep them away from fin nippers, and keep them apart from Endler’s if you care about hybrids.

Livebearer

Endler’s livebearer

Poecilia wingei

Males stay around 1 inch, glow in neon patterns and thrive in hard alkaline water. 8 to 10 males give you color from the first week.

Adult size: 1 in (2.5 cm)
Group size: 8-10 males
Temperature: 75-86°F (24-30°C)
pH / GH: 7.0-8.5 / 15-35 dGH
Temperament: Active, peaceful
Best shape: Long or high

Shrimp: RiskyBioload: LowDifficulty: Easy

Watch out: Males only. Mixed sexes become a colony. They hybridize with guppies.

Livebearer

Platy

Xiphophorus maculatus

Sturdy, peaceful and available in a lot of colors. A small same-sex group works in a hard-water 20.

Adult size: 2 in (5 cm)
Group size: 4-6, same sex
Temperature: 68-79°F (20-26°C)
pH / GH: 7.0-8.2 / 10-30 dGH
Temperament: Very peaceful
Best shape: Long preferred

Shrimp: RiskyBioload: MedDifficulty: Easy

Watch out: They breed readily. Specialist guidance says broods of up to 80 fry are not uncommon, with gestation around 4 to 6 weeks. Keep one sex or have a plan for the fry.

Shrimp

Amano shrimp

Caridina multidentata

The big algae picker of the shrimp world, at 2 to 3 inches. Adults are too large for tiny fish to swallow, which makes Amanos the safer shrimp choice with embers or chilis.

Adult size: 2.5 in (6 cm)
Group: 6+
Temperature: 65-82°F (18-28°C)
pH / GH: 6.5-7.5 / 1-15 dGH
Temperament: Peaceful algae picker
Best shape: Either

Difficulty: Easy

Watch out: Larvae need brackish water, so you will not get a colony. They climb out through gaps, so keep the lid tight.

Shrimp

Neocaridina shrimp

Neocaridina davidi (cherry and other color morphs)

Hardy shrimp that breed in the tank. Thick moss and plant cover give shrimplets a chance.

Adult size: 1.1 in (2.8 cm)
Group: 10 to start
Temperature: 61-82°F (16-28°C)
pH / GH: 6.5-8.5 / 6+ dGH
Temperament: Peaceful, breeds in tank
Best shape: Either

Difficulty: Easy

Watch out: Most fish here will eat shrimplets. Expect a small colony unless the plants are thick. They need GH 6 or higher, and soft water means failed molts unless you add minerals.

Snail

Nerite snail

Neritina natalensis

Nerites clean glass and hardscape, ignore your plants and do not overbreed. Two is plenty for a 20.

Adult size: 1 in (2.5 cm)
Group: 2
Temperature: 72-79°F (22-26°C)
pH / GH: 7.0-8.2 / 5-20 dGH
Temperament: Peaceful glass and hardscape cleaner
Best shape: Either

Difficulty: Easy

Watch out: They need hard, alkaline water or the shell pits. Under pH 7.0, skip them. Use a tight lid. White egg dots on decor are normal and will not hatch in freshwater.

The nano-species 20 gallon

If you want nano fish for a 20 gallon aquarium and a dense planted display, this is the plan I would build, using the small species this site profiles. 18 celestial pearl danios, 10 chili rasboras and 6 pygmy corys share a pH of 6.5 to 7.0 and a GH of 5 to 8, so the tank needs moderately soft, near-neutral water.

Nano-species meadow

Long preferredPlanted: denseDifficulty: ModerateShrimp: Risky

18Celestial pearl danios
10Chili rasboras
6Pygmy corys

Temperature: 72-79°F22-26°C
pH: 6.5-7.0
Hardness: 5-8 dGH

Temperature ranges (°F), shared window highlighted

60°70°80°90°

Celestial pearl danio

Chili rasbora

Pygmy cory

Dense fine-leaved plants and moss, small open lanes and a tight lid. Load: 29.6 weighted inches against a ceiling of about 30.

Flag: This is the fullest nano plan. Drop the chili rasboras for margin, and never run fewer than 15 CPDs. Test GH before you buy, because the overlap is only 3 dGH wide.

These fish have tiny mouths, and live food gets them eating and into color. Start with microworm cultures for the smallest mouths, and add daphnia for the adults. Feed live food 2 or 3 times a week in amounts they finish in 2 or 3 minutes, and use crushed micropellets the rest of the time.

Other nano species do better as their own project. See the profiles for kubotai rasboras and scarlet badis before you try to fit either in here.

6 complete stocking plans

Pick one plan. They are alternative tanks and do not combine. Each plan shows the temperature, pH and hardness its fish share, and flags any narrow overlap. Counts are editorial starting points.

Plan 1: First Tank Classic

20 longPlanted: easy plantsDifficulty: EasyShrimp: Risky

8Harlequin rasboras
6Panda corys
1Honey gourami (optional)
2Nerite snails

Temperature: 72-77°F22-25°C
pH: 7.0-7.4
Hardness: 5-12 dGH

Temperature ranges (°F), shared window highlighted

60°70°80°90°

Harlequin rasbora

Panda cory

Honey gourami

Nerite snail

Harlequin rasboras fill the middle, pandas work the sand, and the gourami takes the surface under floating plants. Load: 29.7 weighted inches against a ceiling of about 30.

Flag: The pH window is narrow, 7.0 to 7.4, because nerites need hard, alkaline water. If your tap pH sits below 7.0, skip the snails and the window opens to 6.0-7.4. The honey gourami is optional. Drop it for real margin.

Plan 2: Dense Nano

20 long or 20 highPlanted: dense, with mossDifficulty: ModerateShrimp: Risky

12Ember tetras
8Pygmy corys
10Neocaridina shrimp (starter colony)

Temperature: 72-79°F22-26°C
pH: 6.5-7.0
Hardness: 6-8 dGH

Temperature ranges (°F), shared window highlighted

60°70°80°90°

Ember tetra

Pygmy cory

Neocaridina shrimp

The best planted-tank plan here. Moss and fine stems give the shrimp cover, and the corys use the whole tank. Load: 19.2 weighted inches against a ceiling of about 24.

Flag: Hardness is the tight spot. Neocaridina want GH 6 or more, and the pygmy cory range stops near 8, so the window is 6 to 8 dGH. Test GH first. Chili rasboras, 12 to 16 of them, work in place of the embers with the same windows. Embers eat shrimplets, so expect a small shrimp colony.

Plan 3: Unheated Room-Temp

20 longPlanted: open laneDifficulty: EasyShrimp: Risky

10White Cloud Mountain minnows
6Salt-and-pepper corys

Temperature: 68-72°F20-22°C
pH: 6.0-7.5
Hardness: 5-10 dGH

Temperature ranges (°F), shared window highlighted

60°70°80°90°

White Cloud Mountain minnow

Salt-and-pepper cory

No heater, moderate flow and an open middle. White Clouds stay active and the corys use the sand. Load: 24.4 weighted inches against a ceiling of about 30.

Flag: The temperature window is narrow, 68-72°F, and it only works if your room holds that range. Pandas want 72°F or more, so this plan uses salt-and-pepper corys, and nerites are left out for the same reason. Past 72°F the minnows leave their listed range.

Plan 4: Livebearer Garden

20 longPlanted: floating plantsDifficulty: EasyShrimp: Risky

8Endler’s males
6Bronze corys
2Nerite snails

Temperature: 75-79°F24-26°C
pH: 7.0-7.5
Hardness: 15-20 dGH

Temperature ranges (°F), shared window highlighted

60°70°80°90°

Endler’s livebearer

Bronze cory

Nerite snail

Endlers add color at the top, bronze corys work the sand, and nerites handle algae. Load: 26.5 weighted inches against a ceiling of about 30.

Flag: This is a hard-water plan. The GH window is 15-20 dGH, so if your tap is under 10 dGH, use Plan 1 or Plan 2 instead. Otocinclus are left out because their listed hardness tops out near 12 dGH. Keep the Endler’s all male.

Plan 5: Ram Showpiece (advanced)

20 long onlyPlanted: caves and sandDifficulty: AdvancedShrimp: Risky

2Bolivian rams (1 pair)
10Ember tetras
8Pygmy corys

Temperature: 75-79°F24-26°C
pH: 6.4-7.0
Hardness: 1-8 dGH

Temperature ranges (°F), shared window highlighted

60°70°80°90°

Bolivian ram

Ember tetra

Pygmy cory

Sand, caves, driftwood and plants that break sight lines, so the pair never sees the whole tank. Load: 26.9 weighted inches against a ceiling of about 30.

Flag: Rams are below the specialist base here, 36 x 18 in against the long’s 30 x 12, so treat this plan as a stretch. Embers fill the school slot because rummy-nose tetras, the usual ram partner, want 36 inches of length. Keep it to one pair and make small weekly water changes. The temperature window is narrow, 75-79°F.

Plan 6: Betta Plan

20 long or 20 highPlanted: heavy, floating coverDifficulty: ModerateShrimp: N

1Betta (male)
6Panda corys
2Nerite snails

Temperature: 72-77°F22-25°C
pH: 7.0-7.4
Hardness: 5-12 dGH

Temperature ranges (°F), shared window highlighted

60°70°80°90°

Betta

Panda cory

Nerite snail

The betta takes the top, the pandas take the sand, and floating plants give him resting spots. Load: 16.2 weighted inches against a ceiling of about 30.

Flag: The pH window is narrow, 7.0 to 7.4, because of the nerites. Bettas often hunt shrimp, so no shrimp here. Fin-nippers like tiger barbs, serpae tetras and zebra danios shred betta fins, so skip fast nippy schoolers. Keep a backup tank ready, since temperament varies by fish.

Fish to avoid in a 20 gallon

These are the common pet-store traps. Shops sell them small, and they grow into a tank you do not own.

Fish	Adult size	Problem
Common pleco	12 in or more	Outgrows a 20 gallon. Fish sold as common pleco vary, and many grow larger.
Goldfish	6 in and up	Heavy waste, long life and a need for a much bigger tank.
Zebra danio	2 in (5 cm)	Hyperactive. Specialist guidance wants a 36 in base, and a 20 long has 30.
Tiger barb	2.8 in (7 cm)	Nips fins and wants about 31 in of base, more than a 20 long gives.
Swordtail	5.5 in (14 cm)	Wants a base around 48 x 12 in.
Angelfish	About 6 in, taller with fins	Deep body and height. Specialist guidance starts near 100 x 40 x 50 cm.
Bala shark	14 in (35 cm)	Social, fast and far too big.
Oscar	14 in (35 cm)	Needs a much larger tank and heavy filtration.
Rummy-nose tetra	2 in (5 cm)	Specialist guidance wants a 36 in base and clean, mature water. A 20 long is borderline.

Looking for an aggressive, predator or biggest fish?

A 20 gallon does not hold one. The honest options are a single betta, a peacock gudgeon, or a bigger tank. Anything sold as a predator for 20 gallons outgrows it.

How to stock it: order and testing

Cycle first, then add fish in stages and test between each step. Veterinary guidance describes new tank syndrome as ammonia or nitrite poisoning in a tank whose filter bacteria are not established. Do not add the whole plan on day one.

Before day 0
Cycle the tank
Run the filter with an ammonia source until ammonia and nitrite both read 0 within 24 hours of a dose, and nitrate shows up. This often takes 3 to 6 weeks. The readings tell you when you are done.
Day 0
Add the school
Add the whole school at once, since a split group bullies its smallest members. Condition the water, match the temperature and acclimate slowly.
Test ammonia and nitrite on days 3 and 7. Both should read 0.
Day 14
Add the bottom group and snails
Go ahead if ammonia and nitrite read 0 and nitrate sits under about 20 ppm. Feed the corys directly.
Test again on days 17 and 21.
Day 28
Add the centerpiece
Territorial fish go in last, so they claim a spot in a settled tank.
Test on days 31 and 35.
Day 42
Add shrimp
Only if the tank is mature, with moss and plants established.

Any reading above 0 for ammonia or nitrite means stop. Change 30 to 50% of the water and hold the next addition until two tests in a row read clean.

What a 20 gallon needs

The gear is simple. Match filter flow to the fish you keep.

Filter: A sponge filter or a hang-on-back with adjustable flow. Chilis and honey gouramis dislike strong current. Cover the intake for kuhlis, shrimp and tiny fish. Here is the best sponge filter for a nano tank.
Heater: An adjustable heater with a guard, around 75 to 100 W (a common hobby rule is 3 to 5 watts per gallon). Skip it only in the cool plan.
Light: Match it to your plants. Low light and floating plants suit most plans here. See the best light for a planted aquarium.
Lid: A tight lid. Kuhlis, bettas and nerites all leave the tank through gaps.
Test kit: A liquid kit for ammonia, nitrite, nitrate and pH. Test strips are fine for a quick check but not for cycling.

Need the gear? Browse Hygger filters, heaters and lights sized for a 20 gallon. This is an affiliate link, so I earn a small commission if you buy through it, at no extra cost to you.

Fish for a 20 gallon aquarium: FAQ

How many fish can you put in a 20 gallon tank?

It depends on the species. A 20 long holds about 30 weighted inches of calm, slim fish, which works out to one school of 8 to 12 tiny fish, one bottom group of 6 to 8 and an optional centerpiece. Count full groups first, then add adult lengths. The method is above.

What are the best fish for a beginner 20 gallon?

Harlequin rasboras, ember tetras, panda corys and a single betta. They take ordinary tap water in a cycled tank and eat standard foods. Plan 1 puts the first three together with nerite snails and an optional honey gourami.

What is the best centerpiece fish for a 20 gallon?

A single betta is the simplest, and a peacock gudgeon is the easiest colorful alternative. A honey gourami works in a lightly stocked tank. Bolivian rams are a stretch in 20 gallons, and dwarf gouramis carry a disease risk, so I would skip both unless you have a reason.

Can you keep a betta with other fish in a 20 gallon?

Sometimes. Specialist guidance recommends one betta per tank, and temperament varies by fish. Corys and snails are the safest company. Skip fin-nippers and brightly colored surface fish like fancy guppies, and keep a backup tank.

Is a 20 long or a 20 high better for fish?

The long. It has about 25% more floor area and a 30 inch swim lane against 24, with the same water volume. Pick a high only for tiny species like embers, chili rasboras, pygmy corys or a single betta.

Can I add all the fish at once?

No. Add the school first, test ammonia and nitrite on days 3 and 7, and add the next group only when both read 0. Adding everything at once overloads a young filter, and the fish pay for it.

What are the best fish for a planted 20 gallon?

Ember tetras, lambchop rasboras, chili rasboras, celestial pearl danios and pygmy corys. Dense plants give them cover and fine leaves suit their size. Plants take up nitrate but do not add swimming room, so stock to the length of the tank.

Can I keep shrimp with these fish?

Adult shrimp, yes. Amano and Neocaridina can live with small peaceful fish. No fish here is fully safe for baby shrimp, and moss only improves the odds. If you want a colony, keep shrimp alone.

Verdict

Buy a 20 long, stock one school and one bottom group at full group sizes, then stop. My default is Plan 2 for a planted tank and Plan 1 for a first tank. Cycle first, add slowly and test between additions.

Kubotai Male vs Female: How to Tell Them Apart

Adrian XH — Sun, 04 Oct 2026 15:24:04 +0000

You can’t sex a kubotai rasbora (Microdevario kubotai, the neon green rasbora) with certainty from the outside. You can read tendencies. Mature females tend to be larger and deeper-bodied. Males tend to be more compact and more intensely colored.

For other small species, see the nano fish guide.

That’s the answer in three sentences. The rest of this guide shows how much weight each clue can carry, what the original species description does and doesn’t say, and where the evidence stops.

What the evidence supports

A specialist aquarium profile describes the pattern. Females run larger and fuller. Males run slimmer and brighter. These are comparative tendencies, not a measured diagnostic test. Confidence: moderate.

Nobody has published a test that checks external sexing against fish of confirmed sex. So treat every clue below as a lean.

Feature	How to read it	Evidence strength
Adult body profile	A fuller, deeper body leans female. A slimmer body leans male	Moderate
Relative adult size	Female often larger	Moderate
Color intensity	Supporting clue only	Moderate tendency, depends on condition
Fin shape or colored fin borders	No validated shortcut found	Unknown as a sexing method
Young or ambiguous fish	Record sex as undetermined	Conservative recommendation

How to compare your fish

Look at mature fish from the same group, under the same conditions. Compare body profile and relative size together. Don’t judge one fish alone.

This is an editorial recommendation drawn from the available evidence. It is not a validated identification protocol. That matters, because the biggest mistake is turning a vague impression into a certain answer.

Read body shape first. Treat color second.

Why color is only a clue

Color is the first thing most keepers notice, and it’s the weakest clue. It depends on condition and lighting.

A firsthand breeder record from Japan backs this up. The breeder found the sexes difficult to tell apart. The same record documents fish fading temporarily after handling, and it photographs one individual under different lighting. Same fish, different color.

That is direct observation, so confidence in what was reported is high. It’s a small personal record, not a controlled experiment, so confidence in applying it to every tank is moderate.

For more on why colors shift in nano fish, read why nano fish lose color.

What the original description says

Kottelat and Witte described the species in 1999 (Journal of South Asian Natural History 4(1): 49-56). Their description portrays transparent fins. It describes a translucent yellow to greenish-yellow body with golden luminosity in aquarium specimens.

The paper also mentions a slightly pointed pelvic fin. But it describes that as a feature of the species. It doesn’t attribute it to males or to females. So the paper gives you no “pointed male, rounded female” rule. Confidence: high for what the paper contains.

This is a common trap. Species-level fin anatomy gets mistaken for a difference between the sexes. Don’t use fin shape to sex a kubotai.

A full belly doesn’t prove a female

A modestly fuller abdomen fits the female tendency, and a female carrying eggs would look fuller. But that is a biological interpretation. It isn’t a finding that every full-bellied fish is a female. Use the belly together with body depth and size, never alone.

What to do with ambiguous fish

Record young fish and unclear fish as undetermined. That’s the honest label. Don’t convert an ambiguous impression into a certain sex assignment.

For tank size, food and tank mates, see the kubotai rasbora care guide. For eggs to fry, see the kubotai breeding guide.

Bottom line

External appearance can suggest sex in mature kubotai. The evidence doesn’t justify certainty for every individual. Read body shape first, use size as a second clue and treat color as a supporting hint. Compare mature fish from the same group, and write down “undetermined” when you can’t tell.

Ember Tetra Care: Tank Size, Lifespan, Tank Mates & Problems

Adrian XH — Sun, 04 Oct 2026 15:00:40 +0000

Ask five ember tetra care guides how long these fish live and you get five answers. 2-4 years. 4-5. 5. 8-10. “10 years or more.” Tank size and group size are just as messy.

This guide covers the ember tetra (Hyphessobrycon amandae). It picks a number for each question, shows where the number comes from, and says plainly where nobody knows.

The gaps are wide. Minimum tank size runs 5, 10, 10-20 and 15 gallons. Group size runs 5+, 6, 8-10, 10-12 and 20-25. Most of those figures get copied from page to page with no source.

So every figure here carries an evidence grade. The numbers come from taxonomic records, peer-reviewed papers, veterinary guidance, modern specialist husbandry and Rolf Meyer’s 1993 Lexikon Süßwasser-Aquarienfische, which holds the most species-specific detail.

How to read the evidence grades

A is strong: taxonomy, peer-reviewed work, authoritative databases. B is good. C is moderate, meaning professional husbandry consensus. D is weak or anecdotal. E is unverified, or there is not enough evidence to say.

Meyer’s numbers count as experienced husbandry, not controlled science. Where he agrees with modern sources, confidence goes up. Where he differs, you see both numbers.

Ember tetra care: quick facts

Fact	Figure
Scientific name	Hyphessobrycon amandae Géry & Uj, 1987
Also called	Amanda’s tetra, fire tetra, dwarf red tetra
Adult size	About 2 cm (0.8 in) standard length
Origin	Rio das Mortes and the Araguaia system, Brazil
Group	8-10 minimum (modern specialist guidance). 10-15 or more is the better target
Tank footprint	At least 45 x 30 cm, about 41 L or 11 US gal (modern specialist guidance). A 60 cm tank is the better start
Temperature	20-28°C (68-82°F) is the listed range. 24-26°C (75-79°F) is the everyday target
pH	5.0-7.0 is the listed range. 6.0-7.0 is the everyday target
Hardness	1-10 dGH
Typical lifespan	2-4 years (the most repeated figure, never verified)

Are ember tetras easy to keep?

Yes, in a cycled, planted tank with a proper group. They are small and peaceful, and most of the care is stable water and tiny food. The catch is that hardiness and diet are still unknown for this species, so nobody has measured how tough they are.

The short version

Keep them in a mature, planted tank about 60 cm long, in a group of 10-15 or more. Aim for 24-26°C and pH 6-7 in soft to moderately soft water. Use a dark substrate, fine-leaved plants and floating cover, and leave open swimming room. Feed tiny food, dry and live. Pick small, peaceful tank mates. Plan on 2-4 years.

Where ember tetra care guides disagree (and what to use)

Published figures split on almost every number. Taxonomic records and specialist books carry the most weight. Keeper anecdotes carry the least.

Topic	Range seen	What to use	Why
Lifespan	2-4, 3-5, 4-5, 5, 5-8, 8-10 years, “10 years or more”	Plan for 2-4. Treat anything past 4 as a bonus	No primary dataset exists. The 10-year claim has no traceable source (E)
Minimum tank	5, 10, 10-20 and 15 gallons	60 cm long, 45-60+ L. The floor is 45 x 30 cm	Specialist guidance gives 41 L. Meyer gives about 40 cm of tank length (C)
Group size	5+, 6, 8-10, 10-12, 20-25	10-15 or more. The floor is 8-10	Specialist guidance says 8-10. Meyer says not fewer than 10 (C)
Temperature	20-28°C (specialist guidance), 24-28°C (reference databases), 24-26°C (Meyer)	24-26°C	Where the sources overlap. No thermal experiment exists (C)
pH	5.0-7.0 (specialist guidance), 6-7 (Meyer)	6.0-7.0	Overlap again. One wild-water report says 5.7-6.2 but was never confirmed (C/D)
Hardness	“GH 0” in some care sheets, 1-10 dGH (specialist guidance), 2-25 °dH (Meyer)	1-10 dGH. Don’t harden the water on purpose	Meyer’s range shows tolerance, not an optimum (C)
Heater	“Essential” in some care sheets, “usually no heater” in others	A stability tool. Use one if the room swings	Editorial guidance, not a study result (D)
Weekly water change	About 10% (Meyer), 20-30% (modern practice)	Enough to keep waste low and chemistry steady	No ember-specific experiment exists (D)
Blackwater and tannins	Stated as fact in several care sheets	Optional	Little is known about the habitat. No physiological need is shown (D)
Betta	“Will work in a heavily planted 10” to “tinier than neons, at risk”	Conditions, not a yes or no. See tank mates	Sources split on 10 versus 15 gallons (D)
Baby shrimp	“Completely shrimp-safe” to “baby shrimp at risk”	Adults usually fine. Shrimplets are at risk	Any small moving animal can be eaten (D)

Some care sheets frame tank size around one fish at 2-3 gallons. They school. A lone ember is a stressed ember, so size the tank for the group.

Some care sheets cite “recent behavioral studies” on betta fin-nipping and name none. Skip that claim.

Some care sheets call the fish hardy and very sensitive to fluctuations in the same article. Both are partly true. Stable water matters more than a perfect number.

What is an ember tetra? Name, origin and size

Name and classification

The fish sold as the ember tetra is Hyphessobrycon amandae Géry & Uj, 1987. Current taxonomic records (updated 13 August 2026) list it as a valid species in the order Characiformes, family Acestrorhamphidae, subfamily Hyphessobryconinae. The type locality is the Rio das Mortes in Mato Grosso, Brazil, and the holotype is MZUSP 37367. Evidence: A.

Older books and some current pages file it under Characidae. A 2024 phylogenomic analysis of 494 species and 1,348 ultraconserved-element loci split the old Characidae into four families, Acestrorhamphidae among them (Melo et al., 2024). The genus Hyphessobrycon is itself non-monophyletic in broad analyses, so more reshuffling is possible. Don’t lose sleep over it. The fish itself hasn’t changed.

Géry and Uj described it in Tropical Fish Hobbyist 35(5):58-61, 65. The issue may have appeared in December 1986, although the bibliographic year is 1987. Hemigrammus amandae is listed as an unaccepted combination. It is the same fish under an old name, not a second species.

The original description compared it with other small Hyphessobrycon, including H. georgettae. Several small South American tetras turn orange or red under aquarium lights, so color alone is a weak way to identify one.

Size

The maximum documented length is 2.0 cm standard length, or about 20 mm. Some aquarium sources quote 2.5-3 cm, and most of that gap is probably standard length against total length, or rounding. Evidence: A/B.

Males and females

Adult males tend to be more intensely colored. Mature females are rounder-bodied, especially with eggs. Meyer adds that males are smaller, slimmer and only slightly more intense in color, at about 1.5 cm against 1.8 cm for females. Treat those as aquarium observations. The 20 mm maximum is better supported. No controlled study of sexual dimorphism in this species turned up. Evidence: C.

Where they live

The native range is Brazil’s Araguaia River basin. No database reviewed here shows an established introduced population anywhere else. Evidence: A.

The original series came from roughly 100 km upstream of the Rio das Mortes confluence with the Araguaia and held only a small number of fish. The natural ecology has never been documented with anything like the intensity of the husbandry.

Specialist accounts place ember tetras in quieter tributaries, backwaters or similar low-flow water rather than the main channel. Specialist guidance says the fish presumably lives in minor tributaries, backwaters and oxbow lakes. A secondhand field account describes shallow water with sand, submerged roots, floating and aquatic plants, and large aggregations of embers. That account was not verified in a peer-reviewed field paper, so treat it as natural history. Evidence for the exact microhabitat: C/D.

The wider drainage varies a lot. Carvalho and Tejerina-Garro measured 25 Araguaia and Tocantins headwater streams and found differences tied to temperature, depth, turbidity and conductivity. “Araguaia water” is not one pH or one conductivity number. That study covered the region, not an ember tetra population. Evidence for variation across the drainage: A.

Ember tetra tank size and how many to keep

Use a 60 cm tank, about 45-60+ L (12-16 US gal), for 10-15 ember tetras. 45 x 30 cm is the smallest footprint any specialist gives.

Run your own tank measurements through our aquarium fish stock calculator to see how your base and school size compare with these benchmarks.

Footprint first, volume second

No experiment has found a minimum tank size for this species. You have two specialist benchmarks. Specialist guidance gives a 45 x 30 cm footprint, about 41 L. Meyer gives a species tank from about 40 cm in length. Both come from experienced husbandry, and no welfare trial set either number. Use them as lower benchmarks.

For a shoaling midwater fish, horizontal space matters more than volume. A tall, narrow 50 L tank does not give the same swimming room as a longer 50 L tank. A standard 10 gallon tank has a smaller footprint than 45 x 30 cm, so measure the tank you own before you trust the gallon number. Evidence: C.

What about a 5 gallon tank?

A 5 gallon tank sits below every specialist benchmark above. One keeper’s guide uses a “5 gallon floor”, and that is a single-keeper figure (D).

Tank	Group	Note
About 40-45 cm, about 41 L	8-10	Lower specialist benchmark (specialist guidance, Meyer)
60 cm, 45-60+ L	10-15 or more	Preferred starting point
Larger, or a mixed community	10-15 or more, plus companions	Size the ember group first, then add tank mates
About 5 US gal	Not advised	Below every specialist benchmark. Single-keeper figures only

How many ember tetras should you keep?

Ember tetras are peaceful, social, shoaling fish. Specialist guidance recommends at least 8-10. Meyer recommends a school of not fewer than 10, and says the broader Hyphessobrycon group looks and behaves better in larger schools. No group-size experiment on H. amandae exists.

There is a close relative case. Saxby and colleagues tested group size in four ornamental fishes. Neon tetras in larger groups darted less, showed less aggression and shoaled more, and groups of 10 showed the strongest shoaling. The authors stressed that the effect varies by species, so this supports the ember advice without proving it.

10 fish is the strongest practical minimum, because Meyer and the modern guidance both land there.
10-15 or more is the better target when the tank and filter allow it.
8-9 sits inside modern advice but is less conservative than the combined evidence.
Very large groups often look better, but no experiment shows where welfare stops improving.
6 may survive. Specialist guidance says 8-10 and Meyer says 10, so 6 is a weak recommendation.

Aggression is described as very low. Chasing, spacing and display inside the group are not a problem by themselves. Evidence that the fish is social: B/C. Evidence for 10 as a practical minimum: C. Evidence that exactly 10 is a proven threshold: none.

If your group hides all day, count them first. See the pale and hiding section below. For more small species that suit the same tank, read our guide to the best nano fish for small aquariums.

Water parameters, temperature and the heater question

Aim for 24-26°C, pH 6.0-7.0 and soft to moderately soft water, roughly 1-10 dGH. Stable beats perfect.

Tolerance is not the same as optimum

No controlled study measured critical thermal limits, chronic pH tolerance, hardness tolerance or long-term welfare in this species. Four ideas get mixed up, so keep them apart.

Source	Temperature	pH	Hardness	What it is
Modern specialist guidance	20-28°C	5.0-7.0	1-10 dGH	Professional husbandry range
Meyer (1993)	24-26°C	6.0-7.0	2-25 °dH	Species-specific husbandry range
Reference databases	24-28°C	not listed	not listed	A referenced ecology value, not an experiment. Their maturity, reproduction and longevity fields are essentially empty
Wild habitat	Warm	Often acidic	Low-mineral	Pointers only. Quantified data from ember localities are poor

Specialist guidance and Meyer overlap closely on temperature and pH. That overlap is why 24-26°C and pH 6-7 make the most defensible target. Evidence: C, strengthened by two independent references agreeing.

Meyer’s 2-25 °dH is much wider than modern advice. It shows that he found the species tolerant in captivity. It does not make 25 °dH ideal. Healthy fish outside the 1-10 dGH band in stable water are no cause for panic, but don’t harden the water on purpose.

KH should be high enough to keep the tank chemically stable, unless you deliberately manage very low alkalinity. No species-specific KH optimum exists (E). Don’t push conductivity down to 20 µS/cm because a field report once measured it.

Captive-bred lines may well tolerate chemistry that differs from a wild collection site, and Meyer’s broad range fits that idea. No controlled multigenerational experiment checked it. “Some aquarium populations tolerate harder water” is a different claim from “hard alkaline water maximizes lifelong welfare.” Evidence for an exact physiological optimum: E.

What the wild numbers actually show

Parameter	What can be supported	Grade
Temperature	A regional dry-season study found many Araguaia headwater streams at 24.1-27.5°C. Not an ember measurement	B for the region, E for the species
pH	A field account reproduced online reports about 5.7-6.2 at ember localities. No independent confirmation	D
Conductivity	The same account reports about 19-29 µS/cm. Not a species requirement	D
GH and KH	No reliable site measurement located	E
Dissolved oxygen	Regional studies measured it. Locality values for embers were not verified	E
Tannins and blackwater	Field-oriented accounts report blackwater. How common it is across the range is uncertain	D
Seasonal variation	Expected in the drainage. One field account reports cooler winter water. No species-specific series	D/E

A conductivity reading can’t be turned into GH or KH without knowing the ions in the water. So “wild embers live at GH 0” is not established by the low-conductivity reports. Evidence for the claim: none.

Do ember tetras need a heater?

Think of the heater as a stability tool. If your room swings in temperature, heat the tank. If the room sits steadily inside 24-26°C, a heater is optional. This is editorial guidance. No study backs it. Care sheets do split. Some call a heater essential and others say most tanks go without.

Keepers ask whether the 70s F are too low, and whether heat feeds algae. Nobody has an ember-specific answer. A regional study found dry-season streams at 24.1-27.5°C, and one field account says winter water runs considerably cooler. Neither is a measurement from an ember population.

Cycling, filtration and flow

A biologically mature aquarium is one of the strongest themes in ember husbandry. Meyer states that H. amandae does best in an older, established tank. Veterinary guidance independently backs mature biofiltration, because ammonia and nitrite from an immature system are a major preventable hazard. Evidence: A for general fish husbandry, C for embers specifically.

Use gentle but effective biological filtration. Specialist guidance considers an air-driven sponge filter adequate and says some current is acceptable. Meyer’s broader Hyphessobrycon advice favors clear, well-filtered water with light movement. Keep the flow gentle enough that tiny fish can hold position and eat without being pushed around. Cycle the tank before the fish go in and keep ammonia and nitrite at zero. Our guide to sponge filters for nano tanks covers the options.

Water changes: the part where sources disagree

No controlled study gives an exact weekly percentage for embers.

Meyer was conservative. He considered the fish most comfortable in a mature, established tank, so he recommended weekly maintenance focused on removing detritus and changing no more than about 10%. Modern practice often uses larger routine changes, especially in heavily stocked or heavily fed tanks.

The evidence supports neither “change exactly 20-30% every week” nor “never change more than 10%.” Change enough water to keep nitrogenous waste and organic load low while holding temperature and chemistry steady. In a lightly stocked, mature planted tank that may be a small change. In a busier community tank it may need to be bigger. Base the amount on waste, stocking, feeding, nitrate and the stability of your replacement water. Evidence for keeping water quality high: A/B. Evidence for an exact ember percentage: D.

Planting, substrate and lighting

Use a dark substrate, fine-leaved plants, floating plants for shade, and open midwater room. Meyer reports the strongest coloration over a dark bottom, among fine-leaved plants, with floating plants shading part of the swimming area. Modern specialist advice matches. Evidence: C.

Substrate

A dark, fine substrate or sand is repeatedly recommended, and Meyer ties a dark bottom to stronger color. No evidence shows it is a physiological need. Treat it as a choice for color and looks. Evidence: C/D.

Leaf litter and tannins

Leaf litter adds structure and supports microbial communities, which may help fry. Tannins can mimic parts of some natural habitats. Specialist guidance lists leaf litter as an optional feature.

Blackwater is optional

Ember tetras do not have a scientifically demonstrated requirement for brown, tannin-stained water. Meyer stresses mature water, a dark substrate, plants and shade, and his entry never makes tannins mandatory. No species-specific clinical evidence shows tannins prevent disease either. A clean, stable, planted tank with sensible chemistry is fine without dyeing it brown.

Lighting

Moderate or subdued light, broken up by floating or emergent plants, is a strong practical choice. Floating cover cuts harsh overhead light and adds visual security. Meyer specifically recommends shading the swimming area to bring out color. No controlled lighting study exists. Evidence: C/D. If you need a light for a planted tank, see our comparison of LED lights for planted tanks.

What do ember tetras eat?

Feed very small complete dry food plus small live or frozen food. The mouth is tiny, so particle size is the limit. Food that enters the tank but can’t be swallowed is not nutrition.

The wild diet is a guess

No gut-content, stable-isotope or feeding-ecology paper on this species turned up. Specialist guidance calls the fish probably micropredatory, eating tiny invertebrates and zooplankton. A modeled trophic level near 3.0 exists, but it comes from close relatives. No ember stomach data went into it. Claims that wild embers eat mosquito larvae, copepods, cladocerans or terrestrial insects are not verified. Evidence: D.

What works in the tank

Meyer’s entry adds species-specific detail. He reports that embers readily take Cyclops and Grindal worms, frozen red mosquito larvae in small portions, frozen white mosquito larvae, and small Drosophila offered at the surface. The practical lesson matters more than any one item. Offer very small prey-sized particles and vary the feeding across the water column, including small moving food. Evidence: C.

Food	Size check	Notes
Micro pellets, finely crushed flakes	If you can’t picture a 2 cm fish swallowing it whole, crush it more	The complete-food base. Slow-sinking suits a midwater fish
Cyclops	Small enough for the mouth	Meyer’s core small food
Grindal worms	Offer small ones	Meyer and specialist guidance both name them
Artemia nauplii	Newly hatched	Modern specialist guidance. Small-food option
Moina	Small	Modern specialist guidance. Small-food option
Frozen red mosquito larvae (bloodworm-type)	Small portions	Reported by Meyer
Frozen white mosquito larvae	Small portions	Reported by Meyer
Drosophila	Small, at the surface	Reported by Meyer. Practical where you have them

Don’t lean on one food. The claim that embers eat only dry micro-food is poor husbandry, and Meyer’s list shows why. If you want to culture your own, read our microworm culture and daphnia culture guides.

How often?

“Twice a day” is common practice. No test backs it. One or two small feeds a day suits adults as long as the total stays sensible. Watch body condition. Chronic excess food rots, raises the organic load and hurts water quality. Evidence for the exact schedule: D. Evidence for a mixed captive diet: C.

Ember tetra tank mates

Pick small, peaceful, non-predatory fish that don’t dominate feeding time and thrive at about the same temperature and chemistry. Judge each one by adult size, predatory capacity, activity level, food competition and environmental overlap.

Meyer reports his own successful experience with three companions. He states that H. amandae can be kept without problems with Boraras maculatus (as Rasbora maculata), Pethia gelius (as Barbus gelius) and small Corydoras. That is not a controlled trial, but it beats an unsourced list from the internet.

Tank mate	Verdict	Conditions
Boraras maculatus	Strong choice	Meyer reports no problems. Similar size, peaceful (C)
Pethia gelius	Strong choice with enough space	Meyer reports no problems. Check temperature and water overlap for your stock (C)
Small Corydoras	Strong choice	Meyer reports no problems. Modern guidance backs small callichthyids (C)
Other small peaceful tetras	Generally fine	Similar temperament. Skip boisterous, fin-nipping or much larger species (C)
Other small rasboras	Generally fine	Modern guidance recommends them. Try chili rasbora or kubotai rasbora (C)
Otocinclus	Behaviorally fine	Peaceful and in a different feeding niche, but it needs its own mature-tank and food care (C/D)
Small gouramis	Conditional	“Gourami” covers very different sizes and temperaments. Some sedate species may work (C/D)
Betta	Conditional, individual-dependent	See below (D)
Dwarf cichlids	Conditional, often workable	Specialist guidance mentions embers as dither fish for Apistogramma. Breeding pairs get territorial (C)
Adult dwarf shrimp	Often coexist	Healthy adults are probably too big to interest an ember. No guarantee (D)
Shrimplets	At risk	A small enough moving animal gets investigated or eaten (D, inference)
Adult snails	Low risk	Eggs and tiny juveniles can’t be guaranteed safe (D)
Large, boisterous or fin-nipping fish	Avoid	Embers are 2 cm. They lose

The absence of reported attacks isn’t a compatibility study. Treat every pairing as a trial.

Can ember tetras live with a betta?

Sometimes. Embers are tiny and a betta may chase or attack them. Betta temperament varies a lot. Keeper answers range from “will work in a heavily planted 10” to “tinier than neons, at risk with a betta.” Advice also splits on whether you need 10 or 15 gallons.

So set conditions instead of hoping. Use a larger tank, dense planting, a proper group of 10 or more, and a calm betta. Individual bettas vary, so nothing here is a guarantee. Evidence: D.

Do ember tetras eat baby shrimp?

Assume yes. Adults often coexist with adult dwarf shrimp, but some care sheets call embers “completely shrimp-safe, ignoring even baby shrimp” and others warn the opposite. The claim “100% shrimp safe” is misleading. If you want shrimplets to survive, give them dense moss and cover, and expect some losses. Evidence: D.

Normal behavior vs problems: pale, hiding, twitching

Pale and hiding fish drive most post-purchase panic searches. Keepers have asked about this for 15 years, in posts titled “hiding like no other”, “lost color” and “ember tetras pale”. The explanations keepers offer are hypotheses, and they are labeled that way below. Evidence for specific causes: D.

A settled group looks like a glowing orange cloud and moves as a tight ball. Fish can look washed-out in the daytime and different at night. That alone isn’t a diagnosis.

What you see	Likely causes	What to check	What to change
Pale on arrival	Shipping stress. Some fish color up, some stay pale for weeks	Ammonia and nitrite. Whether the fish are eating	Give it time and keep conditions steady. Don’t medicate on a hunch
Hiding all day, bolting when you walk up	Group too small. Bright or open tank. Light too close to the water. Tank too small	How many fish you have. Whether there are floating plants and shade	Build the group to 10 or more. Add floating plants and a dark substrate. Lower the light. Keepers also suggest dither fish and fasting then feeding to train them (unproven)
One fish paler than the rest	Low social status, or illness (the keeper “alpha” idea)	Does it eat, swim with the group and breathe normally?	If it acts normal, status is likelier. If it stays apart or stops eating, treat it as a health issue
One or two fish hiding for hours and twitching	Stress, parasites, water chemistry	Flashing, rubbing, white spots, ammonia and nitrite	Fix water first. See the health section
Pale in the day, fine at night	Normal color change at night (keeper idea, unproven)	Look again after lights out	Nothing, if the fish look healthy
Whole group washed-out	Hard or alkaline water. Ammonia or nitrite. Bright, pale surroundings	Test kit readings. The tank background and substrate	Move toward stable, soft to moderately soft water. Add a dark substrate and shade
Sudden deaths after adding new fish	A poisoning or water event	Ammonia, nitrite, new stock, shared nets	Test the water before you do anything else. Quarantine new fish

One keeper lost five embers kept for two years alongside new fish and suspected a poisoning event. That is anecdote, but it fits the same advice: test the water first.

For more causes that hit other nano species, read why nano fish lose color and why my galaxy rasboras died.

How long do ember tetras live?

Plan on 2-4 years. That figure is the most repeated, and nobody has verified it.

Keepers who lose fish around the two-year mark often blame themselves. Check the water first, then consider age.

Online sources variously say 2-4 years, 3-5, 4-5, 5, 5-8 and 8-10, and a few say “10 years or more”. No reliable maximum-age dataset, cohort study or studbook backs any of them. The captive lifespan of Hyphessobrycon amandae is insufficiently verified. Evidence: E.

The long claims look weak. The “10 years or more” claim has no traceable source, which tells you how many citations exist. Other care guides already call it inaccurate.

One keeper with a ten-gallon tank lost embers one by one around 22 months. A reply pointed out that the fish may have been 6 months old at purchase, and that small tetras breed in their first season, so they aren’t built to last. Another keeper asked who has had a first school of 11 all survive past two years.

You can’t know a fish’s age at purchase. So run this check before you blame age:

Ammonia and nitrite read zero.
Temperature holds steady.
No new fish or water event came just before the losses.
The food is small enough to swallow.
The group has 10 or more fish, with no bullying.

If the water is clean and the fish fade slowly after about two years, age is a likely cause. Don’t promise yourself a number. Growth rate is also unmeasured. No useful maturity or growth parameters exist, and no controlled growth study turned up. Evidence: E.

Health, quarantine and medication caution

No convincing study of ember-specific disease turned up, so treat the risks as ordinary freshwater ornamental fish risks. Evidence for ember-specific susceptibility: E.

Aquarium fish can develop ectoparasitic disease (including Ichthyophthirius multifiliis), other protozoal or metazoan parasites, bacterial infections, fungal or oomycete lesions, nutritional disorders, and illness caused or worsened by ammonia, nitrite, wrong temperature, low oxygen or unstable chemistry. Veterinary guidance stresses that poor conditions, organic loading, transport and handling often come before bacterial disease, and that fungal disease is usually secondary.

Signs that need investigation

None of these identifies a pathogen on its own.

Persistent loss of appetite
Rapid or labored breathing
Persistent hiding or isolation from the group
Sustained color loss
Clamped or damaged fins
Flashing or rubbing
Visible spots, ulcers or abnormal coatings
Loss of balance or persistent abnormal swimming
Unexplained weight loss

Prevention that holds up

Establish biological filtration before stocking.
Keep water chemistry and temperature stable.
Don’t allow measurable ammonia or nitrite.
Avoid chronic overcrowding and overfeeding.
Source fish carefully.
Quarantine new fish.
Keep quarantine equipment separate.
Investigate illness before you medicate.

Veterinary guidance recommends a minimum 30-day quarantine for pet fish in general, and notes that quarantine will not catch every pathogen. That is general veterinary guidance with no ember data behind it. Evidence: A/B for the principle. Our breeding guide has a longer quarantine procedure in its quarantine section.

Keepers report that small tetras can be sensitive to salt and medication, including one keeper treating ich on new embers in quarantine. Read the product label, don’t guess doses, and ask an aquatic vet when you’re unsure. Routine “preventive” antibiotics without a diagnosis aren’t evidence-based care and can cause new problems. This guide gives no treatment protocols.

Buying and acclimating ember tetras

Sellers commonly say most aquarium stock is captive bred. Supplier documentation shows captive-bred embers are in the trade. But no audited dataset gives the share of captive-bred against wild-collected fish worldwide, so “all shop embers are captive bred” can’t be verified. Ask the store where yours came from. Evidence: D.

On the conservation side, the species is listed as IUCN Least Concern, based on an assessment dated 7 November 2018. Evidence: B. The assessment is several years old. The fish is traded commercially, and nothing found shows aquarium collection threatens it. The Tocantins-Araguaia freshwater habitat faces human pressure, and researchers call parts of the region poorly known and seriously threatened. That doesn’t show a decline in this species.

A healthy fish eats and swims with the group. Pale on arrival can be shipping stress, so give it time, but check your water conditions in the same week. Buy 10 or more at once. Use a drip or slow acclimation.

Equipment worth buying

Five items cover it, and all of them serve stable water.

A sponge filter. Air-driven and gentle is enough. See sponge filters for nano tanks.
A heater, if your room swings. See the heater section above.
A light you can dim or shade. See LED lights for planted tanks.
A test kit for ammonia, nitrite and pH.
Separate nets and equipment for quarantine.

Ember tetra breeding, in brief

Specialist guidance describes embers as egg-scattering free spawners with no parental care. Well-conditioned adults can spawn regularly. Eggs or fry may occasionally survive in a dense, mature planted tank, but good survival usually means separating the eggs from the adults. Species-specific science on reproduction is very thin. Experienced aquarium literature fills the gap.

Rolf Meyer gives a detailed protocol that worked for him. It is a documented aquarist method. Nobody has optimized it experimentally.

A breeding pair can go in a tank as small as 5 L.
Water at 2-5 °dH and pH 6.2-6.5, at about 26°C.
Fresh water, strongly aerated beforehand.
Spawning among Myriophyllum or loosely arranged Java moss, with a spawning grid or mesh so adults can’t reach the eggs.
About 30-70 eggs, clear and only weakly adhesive.
Hatching at roughly 36 hours at 25°C.
Fry free-swimming around day 4.
First foods as small as fine pond plankton or rotifer-sized organisms, then Artemia nauplii about a week later.

Don’t label 5 L, pH 6.2-6.5, 30-70 eggs or 36 hours as proven constants. Other breeder reports give different incubation times and slightly different chemistry. The broader breeder consensus is soft, mildly acidic water, subdued light, fine plants, mops or mesh, well-conditioned adults, egg protection, tiny first foods and then Artemia.

Not securely known: age at maturity, the validated spawning temperature, an experimentally determined pH or GH optimum, fecundity by female size or age, development rate against temperature, larval survival curves and how often adults eat eggs. Evidence: C for the egg-scattering habit and for Meyer’s protocol as successful practice. D/E for his egg count and hatch time as universal biology.

Full steps live in the ember tetra breeding guide. For egg identification and hatching, see ember tetra eggs.

Ember tetra care myths, checked

Common claim	Verdict	Why
“Ember tetras need exactly pH 6.0.”	Misleading	No pH optimum has been tested. Modern guidance is broader, and Meyer gives pH 6-7
“They must be kept in blackwater.”	Misleading	Blackwater habitat is reported, but no dependence on tannins is shown. Meyer stresses mature water, dark substrate, plants and shade
“Their water must be below 30 µS/cm.”	Misleading	One weakly verified locality reading is not a captive optimum
“GH must be zero.”	Contradicted by husbandry evidence	Conductivity isn’t GH. Specialist guidance gives 1-10 dGH, and Meyer reports success across 2-25 °dH
“25 dGH is ideal because Meyer lists it.”	Misleading	His range is captive tolerance, not a tested optimum
“24-28°C is the proven optimum.”	Misleading	No ember thermal experiment exists. Meyer’s 24-26°C overlaps modern guidance
“A 10 gallon (40 L) tank is the biological minimum.”	Uncertain	About 41 L is a credible benchmark, and Meyer gives about 40 cm. Neither is a welfare threshold
“Six ember tetras is enough.”	Weak recommendation	Six may survive. Specialist guidance advises 8-10 and Meyer says not fewer than 10
“Ten is the proven minimum school.”	Misleading	It is the strongest practical advice because sources converge. No ember group-size experiment proves it
“Larger groups are proven to reduce ember stress.”	Reasonable but indirect	The effect is shown in neon tetras and some other social fishes, not in H. amandae
“Change exactly 20-30% every week.”	Too rigid	No species-specific experiment sets a percentage
“Never change more than 10%.”	Too rigid	Meyer’s 10% is a method for established tanks, not proof that bigger stable changes harm
“Embers are 100% shrimp safe.”	Misleading	Small adults may coexist, but shrimplets are plausible prey
“Bettas are always safe tank mates.”	Misleading	It depends on the betta, the tank geometry and the individual
“They live 2-4 years.”	Uncertain	Secondary sources disagree and no strong primary longevity dataset exists
“Feed exactly twice every day.”	Reasonable convention, not law	Quantity, particle size, food quality, body condition and water quality matter more
“They only eat dry micro-food.”	Poor husbandry claim	Meyer reports Cyclops, Grindal, mosquito larvae and Drosophila
“Captive-bred embers live best in hard alkaline water.”	Uncertain	Broader tolerance is plausible. No long-term welfare experiment shows hard alkaline water is optimal
“Tannins are essential to prevent disease.”	Unverified	No species-specific clinical evidence shows it

What nobody knows yet

For a fish this common, the gaps are big. A large share of ember care rests on accumulated aquarist experience. Controlled science covers little of it. Hardiness and diet are still labeled “unknown” even in specialist guidance.

Field ecology: replicated pH, conductivity, GH, alkalinity, dissolved oxygen, depth, current, substrate, canopy and seasonal temperature from confirmed H. amandae populations. This includes natural water chemistry across the range.
Physiological tolerance: chronic tests of temperature, pH, hardness, conductivity and oxygen, using welfare endpoints and not just survival.
Social welfare: controlled comparisons of group size, tank dimensions, cover and density with validated stress and behavior measures. That covers the biological minimum group and tank size.
Natural diet: stomach-content, metabarcoding or stable-isotope work.
Reproductive biology: maturity, fecundity, spawning periodicity, egg size, developmental rates and larval survival.
Growth and longevity: cohort growth curves and a documented captive maximum age.
Disease: how common illness is in embers, and how susceptible they are, instead of generic freshwater lists.
Trade: wild-caught against captive-bred volume and origin.

Ember tetra care at a glance, with evidence grades

Care factor	Best-supported recommendation	Evidence	Basis
Identity	Hyphessobrycon amandae Géry & Uj, 1987	A	Taxonomic records
Native range	Araguaia basin, Brazil. Type locality Rio das Mortes, Mato Grosso	A	Taxonomic records, Meyer
Adult size	About 20 mm standard length. Meyer lists 1.5 cm males and 1.8 cm females	A/B, plus C	Reference databases, specialist guidance, Meyer
Tank footprint	60 cm long preferred. 45 x 30 cm and about 40 cm are lower benchmarks	C	Specialist guidance, Meyer
Group size	At least 10, preferably 10-15 or more	C	Meyer, specialist guidance, neon tetra experiment
Temperature	24-26°C. Broader specialist range 20-28°C	C	Meyer, specialist guidance, reference databases
pH	About 6-7	C	Meyer, specialist guidance
GH	Soft to moderately soft, about 1-10 dGH. Meyer reports 2-25 °dH tolerance	C	Specialist guidance, Meyer
KH	No species-specific optimum known	E	No adequate primary evidence
Blackwater	Optional, not shown to be mandatory	D/C	Natural-history accounts, specialist guidance, Meyer
Filtration	Mature biological filtration, gentle flow	A general, C species	Veterinary guidance, specialist guidance, Meyer
Plants and cover	Dark substrate, fine plants, floating shade, open swimming room	C	Meyer, specialist guidance
Water changes	Keep water quality excellent. Exact percentage unproven. Meyer used about 10% weekly in mature tanks	A/B general, C/D amount	Veterinary guidance, Meyer
Captive diet	Tiny complete dry food plus small live or frozen food. Cyclops and Grindal best supported	C	Meyer, specialist guidance
Natural diet	Probably micro-invertebrates and zooplankton, not directly shown	D	Specialist guidance, modeled reference data
Tank mates	Boraras maculatus, Pethia gelius and small Corydoras are the strongest direct examples	C	Meyer
Feeding frequency	1-2 small feeds a day is reasonable, not a law	D	General husbandry
Quarantine	General veterinary advice: at least 30 days	A/B general	Veterinary guidance
Breeding method	Soft, mildly acidic water, plant or moss spawning, protect eggs, tiny first foods	C	Meyer, specialist guidance
Meyer breeding values	2-5 °dH, pH 6.2-6.5, about 26°C, 30-70 eggs, about 36 h hatch at 25°C	C as protocol, D/E as universal biology	Meyer
Lifespan	Insufficiently verified	E	Conflicting secondary estimates
Conservation	IUCN Least Concern, assessed 7 Nov 2018	B	Conservation assessment
Captive-bred share of trade	Captive breeding occurs. Global share unknown	D	Commercial evidence, no audited statistics

13 facts you can rely on

The ember tetra is validly identified as Hyphessobrycon amandae Géry & Uj, 1987.
It is native to Brazil’s Araguaia River basin, with its type locality in the Rio das Mortes system.
It is tiny, about 20 mm standard length. Meyer describes males around 1.5 cm and females around 1.8 cm.
It is peaceful and social. Ten or more is the strongest practical group, because Meyer says not fewer than 10 and modern guidance says 8-10.
A mature, biologically stable tank is strongly supported, and Meyer favors established tanks for this species.
24-26°C and pH 6-7 are especially defensible targets, because Meyer and modern professional guidance overlap closely.
A dark substrate, fine-leaved plants and floating shade with open swimming room are among the best-supported layout choices.
No science shows blackwater or tannins are mandatory.
Meyer gives direct aquarium support for Boraras maculatus, Pethia gelius and small Corydoras as compatible tank mates.
Small food matters most. Meyer reports Cyclops, Grindal worms, mosquito-larva foods and Drosophila, and modern care adds micro-foods, Artemia nauplii and Moina.
No experiment proves an exact water-change percentage. Meyer’s 10% weekly method belongs to his mature-tank approach.
General fish-health evidence strongly supports clean water, mature biofiltration and quarantine.
The reported conservation status is Least Concern, from a 7 November 2018 assessment.

Ember tetra care FAQ

Are ember tetras easy to keep?

Yes, in a cycled, planted tank with a proper group. They are small and peaceful, and most care is stable water and tiny food. Hardiness and diet are still unknown, so easy has limits.

How many ember tetras should I keep together?

Keep at least 10, and 10-15 or more if space allows. Specialist guidance says 8-10 and Meyer says not fewer than 10. No ember experiment proves a threshold, but neon tetras shoaled most strongly in groups of 10.

What size tank do ember tetras need?

A 60 cm tank of about 45-60+ L suits a group of 10-15. The lower specialist benchmarks are 45 x 30 cm (about 41 L) and about 40 cm of tank length. Footprint matters more than gallons.

How long do ember tetras live?

Plan on 2-4 years. That is the most repeated figure, but no primary dataset backs any lifespan claim. Longer numbers such as “10 years or more” are weakly sourced. Rule out water problems before you blame age.

Can ember tetras live with a betta?

Sometimes, under conditions. Use a larger tank, dense planting, a group of 10 or more and a calm betta. Betta temperament varies, and embers are tiny. Advice splits on 10 versus 15 gallons, so watch closely.

Do ember tetras eat baby shrimp?

Assume they can. Adult dwarf shrimp often coexist with embers, but shrimplets are at risk because any small moving animal can be eaten. Dense moss and cover help some survive.

Do ember tetras need a heater?

Treat a heater as a stability tool. Use one if your room temperature swings. If the room stays steady within 24-26°C, a heater is optional. Care sheets split, and no ember study settles it.

What do ember tetras eat?

Tiny complete dry food plus small live or frozen foods. Meyer reports Cyclops, Grindal worms, mosquito larvae and small *Drosophila*. Modern guidance adds Artemia nauplii and Moina. Match particle size to a very small mouth.

Why are my ember tetras pale or hiding?

Common causes are shipping stress, a group under 10, bright or open surroundings, hard or alkaline water, ammonia or nitrite, social status and illness. Test the water first, build the group and add floating plants.

Are ember tetras aggressive or fin nippers?

No. Descriptions of the species report very low aggression, and chasing inside the group is normal spacing or display. The bigger risk is the reverse: being chased by a betta or another boisterous fish.

Bottom line

Keep 10-15 or more embers in a mature, planted 60 cm tank at 24-26°C and pH 6-7. Give them a dark substrate, fine-leaved plants, floating shade and open water. Feed tiny food, dry and live. Plan on 2-4 years.

Meyer’s 2-25 °dH range and about 10% weekly water change are records of what worked for him, not universal optima. They do show the fish is more adaptable in captivity than ultra-soft-water care sheets suggest, while still doing best in stable, non-extreme water. If you plan to breed them, start with the ember tetra breeding guide.

Evidence note: This guide is our own review of the species record. Taxonomy, range and size rest on peer-reviewed work and taxonomic records. Practical husbandry rests on modern specialist guidance and on Rolf Meyer’s long experience with the species, which is experience and not a controlled experiment. Care-sheet consensus is not scientific evidence, and a keeper’s long experience is not worthless just because nobody ran a trial.

References

Peer-reviewed work

Géry, J. and Uj, A. (1987). The ember tetra: a new pygmy characid tetra from the Rio das Mortes, Brazil, Hyphessobrycon amandae sp. n. (Pisces, Characoidei). Tropical Fish Hobbyist 35(5):58-61, 65.
Melo et al. (2024). Phylogenomics of Characidae, a hyper-diverse Neotropical freshwater fish lineage, with a phylogenetic classification including four families (Teleostei: Characiformes). Zoological Journal of the Linnean Society 202(1), zlae101.
Carvalho, R. A. and Tejerina-Garro, F. L. (2015). The influence of environmental variables on the functional structure of headwater stream fish assemblages: a study of two tropical basins in Central Brazil. Neotropical Ichthyology 13(2). DOI 10.1590/1982-0224-20130148. Regional data, not an ember habitat study.
Saxby, A., Adams, L., Snellgrove, D., Wilson, R. W. and Sloman, K. A. (2010). The effect of group size on the behaviour and welfare of four fish species commonly kept in home aquaria. Applied Animal Behaviour Science 125:195-205. DOI 10.1016/j.applanim.2010.04.008. Neon tetra evidence, not an ember experiment.

Specialist husbandry

Meyer, Rolf (1993). Lexikon Süßwasser-Aquarienfische: 700 Arten, Haltung, Pflege, Zucht. Bechtermünz/Weltbild Verlag. Entry on Feuersalmler / Funkensalmler, printed p. 146. The author biography says Meyer kept and bred most of the species described.

Medaka Ricefish (Japanese Ricefish): Expert Care Guide

Adrian XH — Sat, 03 Oct 2026 18:55:46 +0000

Medaka ricefish are tough little fish that live without a heater in most homes. This guide covers tank size, temperature, food, breeding and the indoor or outdoor question. Japanese ricefish is the same fish, so you are in the right place.

Medaka also appear in the best nano fish comparison.

The numbers come from a 2008 catalog by Medaka no Yakata, a Hiroshima breeder that kept tens of thousands of medaka. I read it cover to cover. Every temperature, tank size and feeding rule below is theirs.

Quick facts	Details
Scientific name	Oryzias latipes
Ricefish size	Up to 4 cm (1.6 in)
Starter tank	30 cm (12 in) container, 10 fish
Space per fish	1 L (0.26 gal)
Best growth temperature	25 to 28°C (77 to 82°F)
Tolerated range	0 to 38°C (32 to 100°F)
pH	Weakly acidic to weakly alkaline
Care level	Easy. Albino and pure black are harder
Outdoors	Yes, with summer shade

What Is a Medaka Ricefish?

Medaka is the Japanese name and Japanese ricefish is the English one. The scientific name is Oryzias latipes. Some shops sell them as killifish, but they belong to a different group.

They come from Japan and East Asia, where they live in rice paddies, ponds and slow streams. By the early 2000s wild medaka were listed as endangered in Japan. They are also a standard lab animal in biology.

As pets they are young. A 2007 essay in the catalog says goldfish have 500 years of breeding behind them and koi 300. Ornamental medaka had about a dozen. That is why new colors keep showing up.

Medaka Tank Size

Bigger is better because more water keeps the temperature steadier and the water cleaner for longer. A big tank is harder to net and slower to clean.

Start with a 30 cm (12 in) container and 10 fish. That is the catalog’s beginner advice for any medaka fish tank.

The stocking rule is 1 L (0.26 gal) of water per fish. Pack in more and oxygen drops, growth slows and eggs drop.

Setup	Fish	Note
30 cm (12 in) container	10	Starter size
40 L (10.6 gal) tank	Up to 40	1 L per fish
60 cm (24 in) tank	50 to 60	Catalog ceiling
Ceramic pot or foam box, outdoors	1 L per fish	Slow temperature swings

Medaka Temperature: Do They Need a Heater?

Most homes do not need a heater. Medaka tolerate 0 to 38°C (32 to 100°F), so a normal room or a sheltered outdoor tub works. You only add heat to breed in winter or to keep fish active indoors, and then you set it to 20°C (68°F) or more.

Temperature	What happens	When it matters
0 to 38°C (32 to 100°F)	Fish survive	Tolerated range, not a target
25 to 28°C (77 to 82°F)	Most active, best growth	Summer, and fry you want to grow fast
20°C (68°F) and up	Spawning starts, with 12 to 14 hours of light	April to September
Around 17°C (63°F)	Disease risk peaks	April, May, September, October
Near 38°C (100°F)	Dangerous	Small pots in full sun

Here is the trade-off. Warm water makes medaka busy. They eat more, spawn more and make more waste. Waste turns into ammonia, so the water goes bad faster. Cool water makes them quiet. In winter they sit on the bottom and need no food and almost no water changes.

Guides disagree because they answer three questions with one range. Surviving, growing and spawning each have their own number.

Sudden swings make fish sick, so float new fish in a bag first. In very cold regions the catalog says to bring fish indoors and heat the water.

Water Parameters

pH: Weakly acidic to weakly alkaline. 7 is neutral. Tank water drifts acidic over time.
Chlorine: Tap water has it and it harms medaka. Let a bucket stand for a day and night, or use a dechlorinator.
Ammonia, nitrite, nitrate: Bacteria turn ammonia into nitrite and then nitrate. Ammonia is very harmful. Nitrate is milder but builds up. A new tank can hide ammonia in clear water.
Water changes: Change 1/4 to 1/3 at least once a week. Cut back once the tank is stable. Skip them in winter.
Salt: Coarse salt at 0.3 to 0.5% (3 to 5 g per L) is for sick fish only.

How to Set Up a Medaka Tank

Pick a container. Ceramic pots and foam boxes hold temperature best outdoors. Glass is better when you want to watch from the side.
Lay sand on the bottom. Bacteria live in it and break down waste. The catalog likes Oiso sand and baked akadama soil.
Add plants. Water lily, water hyacinth and anacharis all work. Wash them first. Snails and pests ride in on plants.
Fit a filter. A bottom filter with an air pump works. Bacteria also live in sponge and filter media. Our guide to the best sponge filter for a nano tank covers the options.
Add light. Indoor fish miss sunlight and can get vitamin A and D deficiency. Run a lamp.
Fill with aged water. Let tap water stand for a day and match the temperature.
Add the fish. Float them in a bag and mix in tank water in small amounts. That avoids pH and temperature shock.

Don’t overpack the plants. The breeder lost a whole batch of fry in one night in his first hatching tank. Plants use oxygen in the dark.

Indoor Tank vs Outdoor Tub

The catalog recommends outdoors. Sunlight keeps fish healthier and growing faster. Indoors wins for watching them.

Factor	Indoor tank	Outdoor tub or pond
Pros	See fish from the side. Breed all year with a heater and lamp	Sunlight. Live food drifts in. Fish cope with a week without feeding
Cons	Needs a lamp and a filter. Low light makes fish sick	Summer heat. Rain floods. Dragonfly larvae eat fry

A medaka fish pond can be as small as a ceramic water lily pot. In summer, shade it with a reed screen. In rain, leave room below the rim so fish don’t wash out.

Overwintering is simple. Use a big pot or foam box. Add lots of sand and hiding spots like stones, tiles and driftwood. Cut food in October and November and stop in December. Restart in late March when the fish come to the surface. The catalog’s months fit Hiroshima, so shift them for your climate.

Don’t move indoor fish outside in March. The weather swings too much.

Medaka Fish Food: What Do Medaka Eat?

Medaka eat almost anything small, like plankton, daphnia, mosquito larvae and tiny insects. Outdoor tubs grow some of this on their own, but not enough.

Your staple is a prepared medaka food. Live food is better for growth. The catalog names daphnia, tubifex worms, bloodworms and brine shrimp. They cost more. Our daphnia culture guide shows how to grow your own.

Feed what they finish in 5 minutes. Leftover food rots and makes ammonia.

Summer: 2 to 3 times a day
Spring and autumn: once a day
Winter: none

Fry start eating 3 to 5 days after hatching. Use powder-fine food, in small amounts 2 to 3 times a day. You can culture microworms for fry as a live option.

Going away for a week? The fish are fine. Outdoor tubs have mosquito larvae to snack on.

Medaka Tank Mates

Other medaka are the safe pick. You can mix varieties in one tank. Slow eaters like small-eye, albino and daruma types need extra food.

Avoid:

Dragonfly larvae, which eat fry
Adult medaka in the fry tank, because parents eat hatchlings
Unwashed plants, which carry snails and pests

If you mix varieties and collect eggs, the dominant types take over after a few generations.

Male vs Female Medaka

Check the anal fin on the belly near the tail. Males have a bigger fin shaped like a parallelogram. Females have a smaller trapezoid fin.

Only the male’s dorsal fin has a small notch.

Daruma types are harder at first, so use the same fin check. If the anal fin is unclear, check the back too.

Breeding Medaka: The Basics

One male and one female can pair up, but 10 fish with slightly more females works better.

Outdoors they spawn from April to September. Two things trigger it, water at 20°C (68°F) or higher and 12 to 14 hours of daylight. Underfed fish skip spawning or lay fewer eggs.

You can fake summer indoors. Set a heater to 25 to 28°C (77 to 82°F) and run a lamp 14 hours a day.

Females stick the eggs on plants. Parents eat hatchlings, so move the eggs to a separate container with the plant.

Eggs hatch in 7 to 10 days at 25°C (77°F). Colder eggs hatch slower and grow mold. Good eggs are clear and firm. Bad eggs are white and mushy. Pick them out before mold spreads.

Temperature also sets body shape. Keep half-daruma eggs at 27°C (81°F) or higher and about 90% of the fry turn out daruma. Cooler eggs give half-daruma. For daruma pairs the catalog holds fish and eggs at 28 to 32°C (82 to 90°F).

Keep fry apart from adults until they reach 1 cm (0.4 in). Sort them by size. Fast growers bully the small ones, and some breed at 2 months.

Popular Medaka Varieties

Youkihi: Scarlet. Yellow when small and red from medium size.
Miyuki: A platinum glow on the back. One shown in 2007 got brighter within 5 months.
Pure black: Jet black with tiny eyes. Delicate and for experts.
Hikari: Shiny back and a diamond tail.
Daruma: Short and round. The catalog calls it the most popular shape.
Samurai: Dorsal fin split in two, one half raised like a sail.
Albino: Red eyes. Harder to raise.

Beginner pick: half-daruma or a rainbow mix. The catalog calls half-daruma hardier than daruma, and the rainbow mix easy to keep and breed.

Common Medaka Problems and Fixes

Problem	Cause	Fix
Fish sit on the bottom and refuse food	Bad water or disease, if it is not winter	Change water and check the fish
White dots, cotton fuzz or ragged fins	Disease, mostly around 17°C	Fish medicine, or a 0.3 to 0.5% salt bath at 28°C (82°F)
Fry vanish overnight	Night oxygen loss, hydra, dragonfly larvae	Fewer plants, more sun
No eggs	Under 20°C, short days, poor food	Fix light, heat and feeding
Eggs don’t hatch	Infertile or moldy eggs, cold water	Remove white eggs and keep water at 20°C or above
Summer overheating	Small pot in full sun	Shade and move the pot

Medaka Ricefish FAQ

Do medaka need a heater?

No. They tolerate 0 to 38°C (32 to 100°F). Use a heater only for winter breeding or in very cold regions.

How cold can medaka fish tolerate?

The catalog gives 0°C (32°F) as the low end. In winter they go dormant and need no food.

How many medaka fit in a 40 L (10.6 gal) tank?

Up to 40 by the 1 L rule. Start with 10.

Can medaka survive winter outdoors?

Yes, in a big pot or foam box with sand and hiding spots. Bring them in if winters are harsh.

How big do medaka get?

Up to 4 cm (1.6 in).

Are medaka good for beginners?

Yes. Pick half-daruma or a rainbow mix.

Start with 10 fish in a 30 cm container and keep it out of the summer sun. Once that works, pick your first color in our guide to medaka varieties.

Sources: Medaka no Yakata catalog No. 7 (Hiroshima, February 2008). FishBase, Oryzias latipes, for adult size.

Chili Rasbora Care: Tank Size, Food & Tank Mates

Adrian XH — Thu, 01 Oct 2026 12:43:57 +0000

Chili rasboras need a mature tank with soft water. Give them plants, gentle flow and a proper group. And check that their food is small enough to eat.

For your first setup, I recommend at least 45 litres and a swimming length of 45 cm or more. Start with 10–12 fish. Keep the temperature stable at 25–26°C. Give them shaded areas and leave open space for swimming.

It’s tempting to put them in a very small tank because they’re tiny. But they still need room, steady water and enough companions. Their size doesn’t remove those needs.

The main care reference for this guide is the Boraras brigittae entry in Baensch and Riehl’s Aquarium Atlas, Volume 3. Current species guidance and aquarium welfare references supply the practical details that entry leaves out.

Jump to: Tank size · Water parameters · Food · Tank mates · Troubleshooting

Chili rasbora care at a glance

Care point	Practical starting point
Scientific name	Boraras brigittae
Other names	Chilli rasbora and mosquito rasbora
Adult size	About 1.5–2 cm, roughly 0.6–0.8 inches
Tank size	At least 45 litres, about 12 US gallons, with a generous footprint
Tank dimensions	Aim for a base of at least 45 × 30 cm
Group size	At least 8–10, with 10–12 a sensible starting group
Temperature	Atlas range: 25–28°C. Start around 25–26°C, or 77–79°F
pH	Aim around 6–6.8 for routine care if your water can hold it steadily
General hardness	Soft water. Around 1–6 dGH is a practical target
Ammonia and nitrite	Both 0 mg/L
Flow and light	Gentle flow with shaded areas
Diet	Tiny live or frozen foods plus suitably small prepared foods
Temperament	Peaceful and easily outcompeted
Breeding	Egg scatterer with no parental care

Use these recommendations when planning your setup. Check the seller’s water parameters before bringing fish home and avoid changing the water chemistry overnight.

What is a chili rasbora?

Boraras brigittae is a tiny freshwater fish from southern Borneo. The Aquarium Atlas places it around Banjarmasin and describes slow creeks with plants.

It records both black and white waters. Current species accounts give more detail about shaded blackwater streams and peat swamp pools.

So the useful takeaway is soft water, plant cover and slow flow. Your tank does not need to look like dark tea to provide those conditions.

Adults usually reach about 1.5–2 cm. They spend much of their time around the middle and upper parts of the aquarium.

Look for a slender red body with a dark marking along the side. Fish sold under the same common name can include other Boraras species. Our chili rasbora vs phoenix rasbora guide explains the differences.

Are chili rasboras good for beginners?

They suit a beginner who understands cycling and can keep water stable. I would not use them as the first fish in a newly filled aquarium.

The Atlas gives them a difficulty rating covering keepers with some basic knowledge through more experienced hobbyists. Their small mouths and sensitivity during handling need some attention.

If you want to compare other small species, see our nano fish guide. Choose fish around your water and tank size before choosing them by colour.

Chili rasbora tank size and group size

Tank length matters. These fish need horizontal space to move between plants and other members of the group.

Not sure your tank clears the 45 L mark? Check it with our aquarium fish stock calculator. It uses your real internal dimensions, not the gallon label.

The Atlas recommends 40 cm of aquarium length. Its symbol refers specifically to tank length. For a new setup, I would use the larger 45 × 30 cm footprint described in current species guidance.

A tank holding 45–60 litres gives you more room to arrange cover and manage water quality. Check the actual dimensions. Two tanks with the same volume can offer very different swimming space.

Can you keep chili rasboras in a 5-gallon tank?

I would choose a larger tank for permanent care. A 5 US gallon aquarium holds only about 19 litres before substrate and equipment.

It gives you little margin for a full group, feeding mistakes or changing water chemistry. Adding fewer fish also removes the social group they need.

Is a 10-gallon tank enough?

A standard 10 US gallon tank is about 38 litres. Its length can be useful, but the volume falls below the 45-litre starting recommendation here.

If you are buying a tank, move up to 45–60 litres. Keep the first setup focused on chili rasboras.

How many chili rasboras should you keep together?

Keep at least 8–10. A group of 10–12 is a sensible start in a suitable species tank.

They may spread out once they feel safe. A loose shoal does not mean something is wrong. Males can also hold small temporary territories while displaying or spawning.

Watch the whole group at feeding time. One confident fish eating well does not tell you whether the smaller fish are getting food.

Chili rasbora water parameters

Soft, stable water is the goal. Avoid chasing the lowest number listed in a species profile.

Temperature

The Aquarium Atlas lists 25–28°C. I would start at 25–26°C for routine care, which stays within that range.

Use a thermometer to check the water itself. A heater setting is not a measurement. Keep the aquarium away from direct sun and places with large temperature swings.

pH and GH

The Atlas says soft water but gives no numeric pH or hardness range. Those numbers need another source.

For a practical home setup, aim around pH 6–6.8 with roughly 1–6 dGH. These targets sit within the broader ranges in current species guidance. They are not a prescription for every fish already settled in different water.

Wild habitat values can be much more acidic. Reproducing those extremes is unnecessary for routine care and harder to manage.

KH and water stability

KH helps you understand how strongly the water resists pH changes. Very low KH can let pH fall as acids build up.

Test your tap water before buying fish. If it is hard, plan a consistent water supply. Repeated doses of a pH-lowering product can make conditions harder to manage.

Reverse osmosis water can help you make softer water. But do not use pure RO water without a suitable mineral plan. Measure the finished water and prepare changes the same way each time.

Do chili rasboras need blackwater?

They can live in a clear planted tank with suitable water. Tannins and leaves are optional parts of the setup.

The Atlas reports deeper red colour in peat-filtered water. That observation does not make peat a requirement or guarantee brighter fish.

Leaves also break down. Add them gradually and keep checking water quality. Brown water alone tells you nothing about ammonia, nitrite or hardness.

How to set up the tank

Build shelter around the back and sides. Leave an open lane through the middle so the group can move without staying hidden.

Cryptocoryne, Java fern and moss can provide cover under modest lighting. Floating plants help shade the surface. Keep some surface open for gas exchange and feeding.

A darker substrate can make the fish easier to see. Choose aquarium-safe materials and leave enough access to remove food and waste.

Use gentle filtration

A mature sponge filter is a useful option. Another filter can work if its intake is protected and its flow is gentle.

The fish should be able to hold position without constantly fighting the current. Redirect the outlet or reduce flow if the group stays trapped in one sheltered corner.

Our sponge filter guide for nano tanks covers sizing and setup. Choose filtration for the actual tank and stock.

Cycle the tank before adding fish

Use a fishless cycle and confirm it with water tests. A tank that has been running for a few days is not automatically ready.

Ammonia and nitrite should both read 0 mg/L before fish are added and during normal care. Established plants and surfaces give these tiny fish a more settled environment.

Keep a lid on the aquarium. Leave equipment openings covered where practical.

Chili rasbora food and feeding

Food size is one of the easiest details to get wrong. Chili rasboras are small predators with tiny mouths.

The Atlas lists small live foods and Artemia. In a home aquarium, use tiny live or frozen foods alongside suitably small prepared food.

Food	What to check
Baby brine shrimp	Small enough for adult fish to swallow
Cyclops or other tiny frozen prey	Break up clumps before feeding
Small daphnia	Choose the smallest animals rather than large adults
Microgranules	Watch fish swallow them instead of repeatedly spitting them out
Finely crushed flakes	Use small portions that stay accessible to the group

Start with 1–2 small feeds a day and adjust to what the fish actually eat.

Distribute food across a quiet area. Watch the shy fish as well as the first fish at the surface. Remove leftovers before they collect under plants.

For live food preparation, our daphnia culture guide explains how to maintain a culture. Size-sort the food for these tiny mouths.

What if your chili rasboras are not eating?

First check ammonia, nitrite, temperature and flow. Then check whether the food is small enough.

New fish may also hide or lose access to food around faster tank mates. Try a small portion of familiar food in a calm spot and watch from farther away.

Ongoing refusal to eat, weight loss or abnormal breathing needs investigation. Do not keep adding food to compensate.

Chili rasbora tank mates

A species tank is the simplest starting point. The Atlas also favours keeping them alone while allowing other tiny Boraras as possible companions.

Community stocking needs enough room and overlapping water needs. Peaceful behaviour alone does not make two species a good match.

Possible companion	Main concern
Other tiny Boraras	Match water requirements and allow room for both groups
Adult dwarf shrimp	Match mineral needs. Very small shrimplets may be eaten
Small peaceful bottom dwellers	Check temperature, water chemistry and their own space needs
Faster small schooling fish	They may take food before the chili rasboras reach it
Bettas	Individual behaviour varies. Harassment and predation are possible
Larger fish or fin nippers	Avoid fish that can swallow or repeatedly chase them

Can chili rasboras live with shrimp?

Adult dwarf shrimp can work in a planted tank with compatible water. But shrimp species do not all need the same mineral levels.

Do not force Neocaridina into extremely soft acidic water just to copy a blackwater habitat. And do not describe chili rasboras as completely shrimplet-safe. A tiny animal can still be food.

Can they live with a betta?

I would not make that the default setup. A betta may ignore them, chase them or eat them.

The problem is harder to manage in a small aquarium. If you try a community, have enough cover and a separate established tank ready. Persistent hiding is not a successful pairing.

Bringing new chili rasboras home

Ask the seller about temperature, pH, hardness and the food they currently eat. Also check that the fish are actually Boraras brigittae.

Choose alert fish with intact fins and normal breathing. Avoid buying from a tank with unexplained deaths or visibly sick fish.

Quarantine newcomers in a separate established tank. Veterinary guidance recommends at least 30 days, with separate equipment where possible.

Keep lighting low during transfer. Match temperature and follow acclimation advice suitable for the journey and bag conditions. Long-shipped fish should not automatically sit in opened shipping water for a prolonged drip acclimation.

Avoid adding shop water to the aquarium. Handle these small fish gently and never squeeze them through a net or against the glass.

Weekly maintenance

Start with a weekly water change of about 25%. Adjust the routine using tests, stocking and what is happening in the tank.

Dechlorinate replacement water and match its temperature and chemistry. Prepare it before disturbing the fish.

Use a small siphon and protect its opening so tiny fish or fry cannot disappear down the tube. Remove visible waste without tearing through every planted area.

Rinse filter media gently in removed aquarium water when needed. Avoid replacing all biological media at once.

Keep nitrate low and stable. A rising trend tells you to review feeding, maintenance and stocking even if the water looks clear.

Why are your chili rasboras pale, hiding or dying?

Colour is useful to watch, but it is not a diagnosis. Female fish can be paler than displaying males.

Start with water tests before assuming disease or buying medication.

What you see	What to check first
Pale colour or hiding	Recent move, strong light, small group, chasing and water quality
Fish not eating	Food size, competition, stress and abnormal breathing
Gasping near the surface	Ammonia, nitrite, temperature, oxygen and filter function
Deaths after a water change	Dechlorination, temperature differences and sudden chemistry changes
Fish getting thin	Whether each fish eats, food suitability and signs of illness
Eggs appear but no fry survive	Adult access to eggs, filter intake and first-food size

For gasping fish, increase gentle aeration while checking the cause. If ammonia or nitrite is detectable, use appropriately prepared partial water changes and investigate the filter.

Do not assume every pale fish needs warmer water. And do not raise temperature or add medication without a reason.

Our guide to why nano fish lose colour covers the common environmental causes. Persistent illness or repeated unexplained deaths need qualified fish-health advice.

Male vs female chili rasboras

Males usually show stronger red colour. Mature females tend to be fuller through the belly and may be slightly larger.

The Atlas also describes red markings at male caudal fin tips and red edges on the dorsal and anal fins. Females are described as paler without those red caudal marks.

Use several features together. Age, stress and social position can change how strongly a fish shows its colours.

Breeding chili rasboras and feeding fry

Chili rasboras scatter small numbers of eggs when conditions suit them. They do not guard the eggs or care for the young.

A mature planted tank may produce a few surviving fry. Dense moss gives eggs and young fish places to escape adult attention.

For more control, use a separate established breeding setup with fine plants or mesh protecting the eggs. Prepare microscopic first foods before spawning starts.

The Atlas describes an older continuous breeding method with peat substrate and moving parents between tanks every 2–3 weeks. Your display tank can work without copying that historical method.

In a separate short spawning setup, remove adults before they can eat the first young. Fry are too small to depend on ordinary crushed flakes or newly hatched brine shrimp immediately.

Start with suitable infusoria or Paramecium. Offer larger foods only when the fry can swallow them. Protect filter intakes and keep changes small and carefully matched.

For the full spawning setup, see our chili rasbora breeding guide. Get the display tank stable before adding a breeding project.

Chili rasbora care FAQ

Are chili rasboras easy to care for?

They suit a keeper who understands cycling and stable water. Use a mature planted tank, a proper group and food small enough for their mouths.

How many chili rasboras should be kept together?

Keep at least 8–10. A group of 10–12 is a sensible start in a suitable planted species tank with enough swimming space.

Can chili rasboras live in a 5-gallon tank?

I recommend a larger permanent setup. A 5 US gallon tank holds only about 19 litres and offers little margin for a proper group and stable water. Start with at least 45 litres and a suitable footprint.

What temperature do chili rasboras need?

The Aquarium Atlas lists 25–28°C. A stable 25–26°C, about 77–79°F, is a practical starting point for routine care.

What do chili rasboras eat?

Offer tiny live or frozen foods such as baby brine shrimp, cyclops and small daphnia. Suitable microgranules and finely crushed flakes can form part of a varied diet. Watch the fish swallow the food.

Can chili rasboras live with shrimp?

Adult dwarf shrimp can be suitable when their water requirements overlap. Check mineral needs and provide cover. Very small shrimplets may be eaten.

How long do chili rasboras live?

Plan for several years of care. A precise species-specific lifespan is not established by the main reference used here, so I would not promise an exact number of years.

Why are my chili rasboras losing colour?

Check water quality, lighting, group size and chasing first. New fish can be pale after a move, and females are often less red than displaying males. Colour alone does not diagnose disease.

Care references

The main reference is Hans A. Baensch and Rüdiger Riehl’s Aquarium Atlas, Volume 3, the Boraras brigittae entry on printed page 262 and the care-symbol legend on page 73.

The Atlas supports the size, warm temperature range, soft water, plant cover, diet and handling guidance above. Numeric pH and hardness targets, group size and modern tank recommendations come from the supplementary care research.

Further reading: Boraras brigittae species account, OATA’s rasbora care guidance and Merck Veterinary Manual’s aquarium fish management guidance.

Kubotai Rasbora Expert Care: Size, Tank Mates, Diet & Breeding

Adrian XH — Wed, 30 Sep 2026 14:25:59 +0000

Kubotai rasbora care starts with a mature aquarium and a proper group. Plan for at least 10 fish. Give them a planted tank with a 60 × 30 cm footprint, then choose small companions that suit the same conditions.

Compare kubotai rasboras with other small species in the nano fish species guide.

The green colour gets your attention, but the tank dimensions deserve it too.

Kubotai rasbora care at a glance

Adult size About 2 cm Group 10 or more Minimum tank 60 × 30 cm Temperature 22–26 °C

Care detail	Recommendation
Scientific name	Microdevario kubotai
Also sold as	Neon green rasbora or green neon rasbora
Adult size	About 2 cm (0.8 inch) standard length, excluding the tail fin
Tank footprint	At least 60 × 30 cm (about 24 × 12 inches)
Group size	10 or more
Temperature	22–26°C (72–79°F)
pH	6.0–7.0
General hardness	1–10 dGH
Food	Small prepared foods and suitably sized live or frozen foods
Tank mates	Small, peaceful fish with compatible requirements
Breeding	Egg scatterer. Protect eggs and fry from the adults.

These are practical care recommendations. They aren’t experimentally proven survival limits.

What is a kubotai rasbora?

The accepted scientific name is Microdevario kubotai. Kottelat and Witte originally described it as Microrasbora kubotai in 1999. Both names refer to the same fish.

So an older listing for microrasbora kubotai doesn’t identify another species. Check the full name when buying kubotai fish.

Appearance and adult size

The original description records greenish-yellow aquarium specimens with a glowing golden stripe along the side. The dorsal and anal fins are transparent.

Standard length leaves out the tail fin, which explains why size figures need some care.

Aquarium Glaser gives approximately 2.5 cm without specifying the measurement convention. For a clear size description, use about 2 cm excluding the tail. Don’t turn a measured specimen into a promise that every fish stops growing at exactly that length.

Minimum tank size and group size

My recommendation is to choose the tank by its footprint first because a volume label alone doesn’t tell you its length or width.

You can test your tank against the 60 × 30 cm base and a group of ten with our aquarium fish stock calculator.

At least 60 × 30 cm and lists approximately 54 litres, or 14 US gallons. A named keeper, Christian Splettstößer, independently recommends that footprint with a minimum height of 30 cm.

If you’re comparing tanks, take the dimensions with you. A tall tank and a longer tank can hold similar amounts of water.

Keep at least 10 together. Fishkeeper recommends 10 or more, while Seriously Fish advises 8–10. Buy the aquarium for the group you intend to keep.

Temperature, pH and hardness

Use 22–26°C as the practical temperature range.

The published water guidance is pH 6.0–7.0 and 1–10 dGH. dGH measures general hardness. It isn’t a KH target.

Use those figures when planning your setup. Don’t read either endpoint as a tested boundary between safe and unsafe water.

Setting up the aquarium

Start with a mature tank. Fishkeeper recommends dense planted areas and shaded cover, with moderate water movement. Leave room for the fish to swim. The current should support oxygenation without being severe.

Aquarium Glaser also stresses clean, oxygen-rich water. Regular partial water changes belong in the maintenance routine.

My layout choice would be planted shelter around an open swimming area. Decide where the group will swim before filling every available space with decor.

What do kubotai rasboras eat?

Offer crushed flakes or micropellets that the fish can swallow. Small live or frozen foods can include baby brine shrimp, Cyclops and Daphnia.

Prepared food acceptance has also been documented in a laboratory study. The researchers maintained adult M. kubotai on tropical flakes and/or live Artemia.

But check what your own fish actually eat. Splettstößer reported that his newly acquired wild-caught fish initially struggled with some prepared foods. Live Artemia helped him improve their condition. They accepted more foods after settling in. That was one keeper’s experience with wild fish. It doesn’t establish a live-food requirement for every kubotai.

Watch a few mouthfuls during feeding. Picking food up and swallowing it are different things.

Choosing tank mates

Choose small, peaceful companions with matching care needs. Seriously Fish suggests Boraras naevus, Trigonostigma espei and Pangio species among its options. Treat these as candidates to check against your whole setup.

Each additional species needs its own space and suitable group. The kubotai tank recommendation doesn’t automatically leave room for another shoal.

If the fish you want have incompatible requirements, choose which species the aquarium will serve. A species tank is a straightforward option.

Can kubotai rasboras live with shrimp?

Adult shrimp coexistence has been reported. Splettstößer kept kubotai with Crystal Red shrimp in a mixed aquarium. He also said he couldn’t judge whether baby shrimp were being eaten.

That supports one successful setup. It doesn’t establish safety for every shrimp colony.

My advice is to keep fish separate if preserving shrimp offspring is your priority. Don’t build that plan around a promise of zero predation.

Male versus female

Mature females tend to be fuller-bodied. Seriously Fish describes males as more compact and more intensely coloured.

Use body shape as part of the comparison because colour alone won’t give you a dependable answer for every fish.

How long do kubotai rasboras live?

I couldn’t verify a typical aquarium lifespan from the reliable sources reviewed for this guide.

A precise lifespan number would need documented longevity records. The available care guidance doesn’t provide them. Giving you an unsupported number would add certainty the evidence doesn’t have.

Breeding kubotai rasboras

Kubotai scatter eggs among vegetation and decor. Adults can eat eggs and larvae. Fishkeeper recommends a separate breeding aquarium with fine plants or spawning mops, followed by removal of the adults after spawning.

The fry need very small initial foods. Introduce Artemia nauplii once they can accept them.

Exact hatch times remain insufficiently verified in the research behind this guide. Before setting up a breeding tank, decide how you’ll protect the offspring and feed the smallest fry.

Sources

Research checked on 30 September 2026.

Kottelat and Witte’s original description, 1999. Identity, appearance and standard-length measurements.
Eschmeyer’s Catalog of Fishes, updated August 2026. Accepted scientific name.
Seriously Fish: Microdevario kubotai. Specialist care recommendations.
Fishkeeper: Neon Green Rasbora. Aquarium setup, food and breeding.
Frank Schäfer for Aquarium Glaser, October 2018. Specialist importer guidance.
Conith and colleagues, 2022. Documented captive feeding.
Christian Splettstößer, updated April 2024. Attributed feeding, shrimp and breeding observations.