Fish for soft, acidic water
13 species from the AquaLog care guide · Updated
In short: These fish come from soft, acidic rivers and need pH at or below 7 to thrive. If your tap water is hard, you will need to soften it, usually by mixing in RO water, before keeping them, and keep the change slow and steady.
Many South American and Southeast Asian fish come from blackwater: soft, acidic, tea-coloured water from leaf litter and peat. Every species below has a maximum pH of 7 or lower in the AquaLog care guide.
Do you have the right water?
Test pH, GH and KH. Soft tap water with low KH suits these fish well. Hard tap water means mixing in reverse-osmosis (RO) water, and that's a commitment for every water change. If you'd rather work with hard water, see fish for hard, alkaline water.
The species
| Species | Min. tank | Temperature | pH | Temperament | Group | Care level |
|---|---|---|---|---|---|---|
| Chili rasboraBoraras brigittae | 30 L (8 gal) | 23–28 °C | 4.5–7 | Peaceful | 10+ | Intermediate |
| Clown killifishEpiplatys annulatus | 40 L (11 gal) | 22–28 °C | 4.5–7 | Peaceful | 6+ | Intermediate |
| Licorice gouramiParosphromenus deissneri | 40 L (11 gal) | 24–28 °C | 4–5.5 | Peaceful | 2+ | Advanced |
| Hengel's rasboraTrigonostigma hengeli | 60 L (16 gal) | 23–28 °C | 5.5–7 | Peaceful | 8+ | Intermediate |
| Cardinal tetraParacheirodon axelrodi | 75 L (20 gal) | 24–29 °C | 4.5–7 | Peaceful | 8+ | Intermediate |
| Chocolate gouramiSphaerichthys osphromenoides | 75 L (20 gal) | 26–30 °C | 4–6 | Peaceful | 6+ | Advanced |
| German blue ramMikrogeophagus ramirezi | 75 L (20 gal) | 26–30 °C | 5.5–7 | Peaceful | 2+ | Advanced |
| Five-banded barbDesmopuntius pentazona | 90 L (24 gal) | 23–28 °C | 5–7 | Peaceful | 8+ | Intermediate |
| Rummynose tetraHemigrammus rhodostomus | 90 L (24 gal) | 24–28 °C | 5.5–7 | Peaceful | 8+ | Intermediate |
| Apistogramma agassiziiApistogramma agassizii | 110 L (29 gal) | 24–29 °C | 5–7 | Semi-aggressive | 2+ | Intermediate |
| Blue gularis killifishFundulopanchax sjoestedti | 110 L (29 gal) | 22–26 °C | 6–7 | Semi-aggressive | 2+ | Advanced |
| Panda apistogrammaApistogramma nijsseni | 110 L (29 gal) | 24–29 °C | 4.5–6.5 | Semi-aggressive | 2+ | Advanced |
| DiscusSymphysodon aequifasciatus | 250 L (66 gal) | 28–31 °C | 5.5–7 | Peaceful | 6+ | Advanced |
Keep it stable
Soft water has little buffering (low KH), so pH can drop suddenly. Test regularly, change water on a steady schedule, and make any adjustment gradually over days, not hours. See aquarium water parameters explained.
Several fish here, such as discus and German blue rams, also need warm water (26 °C or higher). Check each species page before mixing them with others.