Hi, I have 5 angel fish. 2 are a fair bit larger than the rest. recently I noticed that one of the larger black ones fins were a bit torn. A day later he seemed to disappear. i couldnt find him amongst the plants or anything, so I presumed he had died and been eaten. This was 2 days ago, and today when I moved my filter out to clean up i found him behind it, still alive. Unfortunately his fins are a lot worse now. Is this fin rot? None of the other fish in the tank have a thing wrong with them.