A week and a half ago, my fish started biting his tail (I'm pretty sure it is tail biting because there are nice clean chunks out of his tail, and it doesn't look like pictures I have seen of fin rot). To try to stop the tail biting (if it is actually tail biting), I have been feeding him a tiny bit more and trying to entertain him (making him flare, putting a ping pong ball in the tank, putting different things outside of the tank). Yesterday, his tail didn't look like it had anymore damage to it, and everything else on him looked totally normal. But today when I checked on him, his tail looked worse, and his right ventral fin was torn in half. I don't know what I'm doing wrong, and I'm really worried about it... There isn't anything in the tank that could cut him, so I'm really confused... Please help!