Over the past couple weeks I have noticed that my Blue Tang, that I have had for a year now, is not looking too good. When I first got the tang, it was the size of a quarter and has tripled in size. He was pretty plump up until recently when I have been noticing him not eating the food I normally feed, but will occasionally nibble a little on some flakes. The tang is getting really skinny and looking pale. Looks like he's shriveling up. Are these signs of a sickness?