An hour or so ago my Clown Loach was swimming and eating. I just spotted it floating at the top of the tank dead. I've had him for a month or so. He lived with a Dojo Loach, Red Fin Black Shark, and assorted Cichlids. I have never seen any of the others bothering it in any way. Swam with them daily. Yesterday, early, I put in a new and stronger filter and the water level was down an inch so I topped it off. As I said, an hour ago it showed no signs of anything wrong. Any ideas?