At least a six foot tank. Doesn't have to be that deep, just lengthy enough for them to swim about when they reach full size. I would get at least six, as they like to shoal. Make sure it has a good cover. They do like to jump. They will grow quickly to about seven inches, then more slowly until they max out around 14 inches. Actually, I just re-read the title of your post.....The IDEAL Bala Shark tank would be much larger. Six foot would be a bare minimum. And it would need to wide for them to turn around.
