Koi fish are addictive

[king2005]

I love koi !! I didn't know you could keep them in a tank though...

Thats because you can't. They are not meant to be kept in typical house tanks. They are large pond fish as they get 1-2 feet long & produce so much waste that they just poison themselves in a typical house tank.
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You cannot keep goldfish in a tank & think it'll grow to its environment. Thats plain ignorant. No animal "grows" to it environment.. Goldfish (and other large species of fish.. like Plecos) will suffer terribly until they die in their death bowls/tank

Goldfish should live 20+years. Not 0.5-5yrs.. Most die so young & so tiny & quite painfully

Same goes for turtles *sigh*