Goldfish tank size
Plan on 20 gallons for the first fancy goldfish and 10 more for each extra one.
That is Aquarium Co-Op’s rule. Ornamental Fish International asks for at least 100 litres (26 gallons) for one and 50 litres (13 gallons) for each additional adult. Single-tailed common goldfish need far more room than either.
How many goldfish fit in each tank
Fancy goldfish only. The bold column is the lower of the two guides, which is the safer number to plan for.
| Tank | Co-Op | OFI | Plan for |
|---|---|---|---|
| 20 Gallon Long | 1 | 0 | 0 |
| 29 Gallon | 1 | 1 | 1 |
| 40 Gallon Breeder | 3 | 2 | 2 |
| 55 Gallon | 4 | 3 | 3 |
| 75 Gallon | 6 | 4 | 4 |
| 125 Gallon | 11 | 8 | 8 |
A 20 gallon tank holds one fancy goldfish by the Co-Op rule and none by the OFI rule. A small bowl meets neither.
Fancy and common goldfish are different
Fancy goldfish have double tails and rounded bodies. Ornamental Fish International says they are unlikely to grow beyond 20 cm (about 8 inches).
Common goldfish have a single tail and a slim body. FishBase records them reaching 48 cm (19 inches) and suggests a minimum aquarium length of 100 cm (39 inches). Seriously Fish treats goldfish as a pond fish. Aquarium Co-Op notes that common goldfish out-compete fancy ones, so keep the two apart.
Water for fancy goldfish
| Optimal temperature (OFI) | 59 to 73°F |
|---|---|
| pH (OFI) | 6.5 to 8.5 |
| Cold water range (Co-Op) | 50 to 70°F |
Tank sizes and weights: 40 gallon breeder, 55 gallon, 75 gallon.
Gear for a goldfish tank
Searches on Amazon for the right size. Check the tank size or flow rating on the listing before you buy.
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Sources: Aquarium Co-Op, Ornamental Fish International, FishBase.