Black Moor shedding a layer of skin!?????

The other day I looked into my tak and my Black Moor looked like it was almost shedding a layer of skin...a very thin layer of white skin was peeling off him, im notsure if it was just something he'd got caught up on but there was nothing in the tank to make me obviously see what it was?? The tank is very clean and it hasnt happened since or before...what the hell was it???