He has been swimming at the top of the tank for a day and a half. He is not interested in food. He use to allows be out in the open on the sand but for the past month or so he has been hiding and I have hardly seen him. I added a randall's pistol shrimp but haven't seen or heard it since I added it three weeks ago. This is my first tank so I am not sure if he looks healthy or not. He doesn't look thin to me. The tank is a year and a half old. I have had him for at least a year. Tankmates are 2 clownfish and a tailspot blenny and CUC. They all seem fine. I have recently developed quite the aiptasia problem but not sure if that would affect him. I tested for ammonia. Salinity is 1.025. I know other tests are necessary but I assume low alkalinity or magnesium wouldn't hurt a fish. But I can test everything if needed. Everything was within range last week except magnesium was a little low.