Not sure if this was the culprit but since some of my SPS suddenly decided to retract their polyps I decided to put him in time out. Normally he would stay on a colony of acro but occasionally he would jump around to other SPS corals. I never saw him actually nip at any corals, only sit on them. Since I put him in the sump I haven't seen much of a change so I don't think he was the problem. Either way, I don't want to chance it. He's actually a cute fish. Look at that pic!