Hi! Last summer my family built a small pond in our backyard. It's eighteen inches deep, by three feet across, by five feet long. (I think this is about 250 gallons?) Ever since we built it, my parents and siblings have been suggesting we get a/some koi. I read the koi profile and discovered that they need 1000 gallons. My parents say that the koi (like goldfish) will grow to the size of the tank, but I think I remember reading that while that is true, it can harm the fish internally. Is this true? Or am I remembering wrong? If it is true, could you please explain it so that my parents can read it? I would hate to put the koi in a tank too small and hurt them. Thank you for helping me!