I have a pond (6'x4' 2.5 Deep)in my basement that currently houses two ID's. ONe is 31", 20 yrs old and the other is 14" 4 years old. They love algae and massivore pellets. Think about a tank that is long and wide. They need to swim, mine have lots of room to turn corners. Depth is not always an asset. They dont swim up and down. Be prepared for big fish. They get big fast if you get them young. I also have a baby 7" that wont be in the pond till he grows a little more.