I know it is about marine fish but I have a koi one koi and one goldfish I thought the koi was a goldfish when I bought it it now as barbells and is a koi I need to know If one koi can live a good life in a tank 300 to 500 gallons a tank:headwally: I don't what to return it because I like the koi and I don't know why I would be sold a gold fish as a koi it looked like a goldfish any body know if I can keep it