Okay, a really silly question would be.. can you keep Koi in a tank or do you have to have a pond for them? Just wondering. I'm probably not getting Koi or anything, just a question... I'm talking like small Koi (of course they would grow but what about while they are small?) Does anybody ever do that? Or are they just strictly an outdoor fish? Thanks for all the help you guys give me!

Last year I rescued some tiny baby koi from our feeder tank at work and kept them in first a 30 gallon tub and then my 100 gallon tank for about 6 months. By the time I moved them outdoors they had more than outgrown that small living area. I would not recommend it and certainly not long term. I compensated for the small tank/tub by doing massive regular water changes so as not to stunt their growth.

Many people think they will keep them indoors till they outgrow their tank but most will be stunted long before they "outgrow" the tank. So in short I would say no, they do much better as outdoor fish. As soon as I moved my koi out to the pond they experienced a growth spurt.

Koi don't like aquariums that well, they are too "open" an environment. These fish grow much faster then goldies do, a good 2 year old should be a minimum of 12" in average growth.

They just fair much better in a pond environment. They are also messier then goldies are .