How Many Common Goldfish in a 40-Gallon Tank?
In a 40-gallon tank you can comfortably keep about too few for a proper school Common Goldfish. As a schooling species, never keep fewer than 3.
Why
Stocking is driven by adult size and waste output, not just fish count. Common Goldfish reaches about 12" with a heavy bioload, and needs 60–72°F water at pH 6.5–8. Always cycle the tank and test water before adding livestock.
| Adult size | 12" |
|---|---|
| Minimum tank | 40 gallons |
| Temperature | 60–72°F |
| pH | 6.5–8 |
| Temperament | Peaceful |
| Schooling | Yes — group of 3+ |
| Diet | Omnivore |
| Care level | Easy |
| Origin | East Asia (domesticated) |
More fish for a 40-gallon tank → Common Goldfish tankmates →