How Many Cardinal Tetra in a 40-Gallon Tank?
In a 40-gallon tank you can comfortably keep about 6–33 Cardinal Tetra. As a schooling species, never keep fewer than 6.
Why
Stocking is driven by adult size and waste output, not just fish count. Cardinal Tetra reaches about 2" with a moderate bioload, and needs 73–81°F water at pH 4.5–6.5. Always cycle the tank and test water before adding livestock.
| Adult size | 2" |
|---|---|
| Minimum tank | 15 gallons |
| Temperature | 73–81°F |
| pH | 4.5–6.5 |
| Temperament | Peaceful |
| Schooling | Yes — group of 6+ |
| Diet | Omnivore |
| Care level | Moderate |
| Origin | Orinoco and Negro river basins |