Fish for small tanks (40 litres / 10 gallons or less)
13 species from the AquaLog care guide · Updated
In short: Only a handful of fish truly suit tanks of 40 litres or less: mostly tiny schooling fish, a few small gouramis and killifish, and a single betta. Small tanks are harder to keep stable, so choose one species, stock lightly and change water every week.
Small tanks look easy but are the opposite: less water means temperature and waste levels change faster, and a missed water change shows up sooner. These are the freshwater fish whose minimum tank size in the AquaLog care guide is 40 litres (about 10 US gallons) or less.
Most are nano schooling fish that need a group, so in practice a small tank holds one schooling species or one centrepiece fish, not a mix of everything below.
The species
| Species | Min. tank | Temperature | pH | Temperament | Group | Care level |
|---|---|---|---|---|---|---|
| BettaBetta splendens | 20 L (5 gal) | 24–30 °C | 6–7.5 | Aggressive | 1 | Beginner |
| Chili rasboraBoraras brigittae | 30 L (8 gal) | 23–28 °C | 4.5–7 | Peaceful | 10+ | Intermediate |
| EndlerPoecilia wingei | 30 L (8 gal) | 22–29 °C | 7–8.5 | Peaceful | 3+ | Beginner |
| Sparkling gouramiTrichopsis pumila | 35 L (9 gal) | 22–28 °C | 6–7.5 | Peaceful | 3+ | Intermediate |
| Celestial pearl danioDanio margaritatus | 40 L (11 gal) | 20–26 °C | 6.5–7.5 | Peaceful | 8+ | Intermediate |
| Clown killifishEpiplatys annulatus | 40 L (11 gal) | 22–28 °C | 4.5–7 | Peaceful | 6+ | Intermediate |
| Dwarf emerald rasboraCelestichthys erythromicron | 40 L (11 gal) | 21–26 °C | 7–8 | Peaceful | 8+ | Intermediate |
| Ember tetraHyphessobrycon amandae | 40 L (11 gal) | 22–28 °C | 5.5–7.5 | Peaceful | 10+ | Beginner |
| GuppyPoecilia reticulata | 40 L (11 gal) | 22–28 °C | 7–8.5 | Peaceful | 3+ | Beginner |
| Licorice gouramiParosphromenus deissneri | 40 L (11 gal) | 24–28 °C | 4–5.5 | Peaceful | 2+ | Advanced |
| Neon green rasboraMicrodevario kubotai | 40 L (11 gal) | 22–27 °C | 6–7.5 | Peaceful | 10+ | Intermediate |
| Pea pufferCarinotetraodon travancoricus | 40 L (11 gal) | 24–28 °C | 6.8–8 | Aggressive | 1 | Advanced |
| Pygmy corydorasCorydoras pygmaeus | 40 L (11 gal) | 22–26 °C | 6–7.5 | Peaceful | 8+ | Beginner |
Which of these should live alone?
The betta is rated aggressive: keep one male per tank. The pea puffer is also aggressive and is best in a species-only tank. Check each species page for its tank mates and fish to avoid.
Shrimp and snails for small tanks
Invertebrates aren't in the table, but several suit small tanks: cherry shrimp and nerite snails from 20 litres, Amano shrimp and mystery snails from 40 litres.
Keeping a small tank stable
- Change 10–25% of the water every week. See how often to change aquarium water.
- Use a heater with a thermostat; small volumes cool and heat quickly.
- Feed sparingly; leftover food fouls a small tank fast.