This question is going to be very vague and I apologize. I have a catfish (I don't remember the species beyond that it had the word green in it) who is involuntarily floating to the surface. When he's active he can swim back down to the bottom but I've notice that when he relaxes he floats back to the top. I remember reading in a book I have but can't find that fish have an organ that regulates their water depth for them and that sometimes it can get unbalanced. Does this sound right and how can I correct it?