Care guide
Caring for goldfish and koi
This guide covers Fancy goldfish and the other species that need the same care. Ask the seller about anything particular to Fancy goldfish.
- Adult size
- About 18 cm
- Water temperature
- 18–24 °C
- pH
- 7–8
- Smallest tank
- 120 litres
- Temperament
- Peaceful
- Care level
- Easy
Goldfish and koi are coldwater fish that grow larger and live longer than most people expect: often 10 to 20 years or more. They need big tanks or ponds and strong filtering.
Room to grow
Fancy goldfish need at least about 120 litres for one or two, with more for each extra fish. Common and comet goldfish and koi belong in ponds. Bowls are never suitable.
Water
Goldfish produce a lot of waste. Use a filter rated well above the tank's size and change water weekly. They don't need a heater in most homes.
Health
Fancy goldfish can have buoyancy problems; feed sinking food and soaked peas. Koi herpesvirus is a serious disease; buy from sellers who quarantine.
Further reading
General information to help you prepare, not veterinary advice. Every animal is different: ask an experienced vet about yours. Reviewed by PerfectPal on November 3, 2026.