150 Gal. wet-dry sump w/ predrilled pre-filter overflows with protein skimmer, Rio 1700 in tank for circulation. Tank has been set up for over 2 years. I've had shark since cycling. Never had any problems until now. I know everyone will say 150 too small, but it's not. He's grown very little in past 6 months and swims fine. Never stressed out. I am going to change water tonight and hopefully he will recover. I put in balance blocks as needed and some calcium as needed. I ran out of testing supplies recently but have lept up on water changes so i'm not sure if that is the problem. I also have a Blue Hippo Tang, Pajama Cardinal fish, and three decent sized damsels. None of these fish or my other shark are showng any ill signs. Maybe he's just going through something right now. I hope. Seeing that Hippos are pretty sensitive, it makes me think that it's something with him and not a water issue. Any thoughts? Tony, about you old shark, was he black and white as a juvenile or is he a different variation?