Question: can koi fish live in a tank?
Answer: Koi grow quickly and get very large. Keep mature koi in an outdoor pond of at least 3 feet deep, with at least 50 gallons of water per fish. Young koi can be kept indoors in an aquarium of at least 29 gallons. ... Whether they live indoors or outdoors, add no more than 3 new koi at a time.