I have a carpenter wrasse in my nano tank for quite awhile now, he has been doing well but when I looked at it this morning, it was lying on its side on the live rock and a few hours later it was lying on the floor. When I tap on the tank, it swam back up. It still eats and comes to the top of the tank during feeding. Can anybody tell me what's wrong? I have a firefish, a clownfish, a banggai cardinal and 2 nassarius snails with the carpenter wrasse in the tank.