help tang

Hello, Been having some trouble with my kole tang bullying or at least we think he is.) When we first put the kole tang it was fine but after awhile we couldn't find our Goby (paired with pistol shrimp) for a day we have lots of hiding spots so i figured I see the goby tomorrow. During the...

powder brown tang looking very bad, seems to be slimming on the bottom of its belly and eye. What to do. I thought my lights maybe to string but I turned them down and still looking shady. A lot of flow and oxygen in the tank. I have other tangs and none of them are experiencing the same.