Photo: Ry362 · CC BY-SA 3.0
Freshwater · Intermediate · 30+ gal
Carassius auratus
Goldfish are coldwater carp, not bowl ornaments. Fancy strains need tens of gallons and strong filtration; single-tail commons belong in very large tanks or ponds.
| Water type | Freshwater |
|---|---|
| Care level | Intermediate |
| Minimum tank | 30 gallons |
| Temperament | Generally peaceful but clumsy. They may outcompete slow fish for food and will eat small tank mates, plants, and anything that fits in their mouth. Not a tropical community fish. |
| Diet | Omnivore with a lot of plant matter. Sinking goldfish pellets as a staple, plus blanched peas, greens, and occasional protein. Avoid cheap floating flakes as the only diet; they contribute to swim bladder issues in fancy strains. |
| Temperature | 65–74 °F |
| pH | 7–8 |
| Hardness / salinity | Moderately hard, alkaline water is typical (around 8–20 dGH). They are coldwater fish, not tropical. |
A goldfish bowl is one of the most persistent pieces of bad advice in the hobby. Goldfish are messy, high-bioload carp that grow far beyond the size of a decorative bowl. Ammonia builds in hours to days in that little water. There is no room for a filter, and temperature swings are harsh.
If you already have a goldfish in a bowl, the kind move is a cycled aquarium with a filter, regular testing, and a realistic adult size in mind — not a slightly bigger bowl.
Hobby consensus splits fancy (round-bodied) goldfish from single-tail commons and comets. Fancy goldfish such as orandas, ryukins, and telescopes are often given 20 gallons as an absolute floor for one fish; 30 gallons for the first fish and about 10 extra gallons per additional fancy is a more responsible indoor plan.
Slim-bodied commons, comets, and shubunkins are active and large. They are pond fish in most cases, or 40–75+ gallons for a single indoor fish — and that is still a compromise. They are a poor fit for a starter 10- or 20-gallon kit.
Over-filter. Canister filters, large hang-on-backs, and sponge filters in combination are common because the waste load is high. Weekly water changes are not optional. Test ammonia, nitrite, and nitrate until you know the tank's rhythm.
Keep them cooler than tropical community fish. Mid-60s to low-70s F is a typical indoor range. Heating a goldfish tank to 78 F so you can add neon tetras is unfair to both.
Goldfish are sold as beginner pets, but the bioload, growth, and long lifespan (often a decade or more with good care) make them a commitment. Swim bladder problems in fancies, poor genetics, and chronic water-quality issues are common in undersized setups.
No. A bowl cannot hold a stable, filtered volume of water for a carp that produces this much waste. Use a real aquarium — tens of gallons, not a centerpiece bowl.
Plan on about 30 gallons for the first fancy goldfish, plus more for each additional fish. Commons and comets need much larger tanks or a pond.
Usually no. Their temperature and mess do not match tetras, guppies, or bettas. Keep goldfish with other goldfish of similar type.
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Pterophyllum scalare
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Min. tank: 30 gal
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