How long have you had him? If the answer is not long, then there is your answer. Plus triggers are shy fish, mine had a rock he would go into and only came out for food...not often would he come out to "just swim"
I have a square anthias, he is doing great...well up until today. I was watching him and noticed he wasen't using the right gill to breath. I think he got stung by the tongue coral he likes to hang out by, butttt I am not sure. He is swimming just fine, even using his right fin...eating just...
I had a angel in my tank, and he did good for awhile...then one day he started eating my corals...it took forever to get him out of my tank and the damage he did wasen't worth it!!! There are certin tangs out there that don't get ich as easy as others, my yellow tang has never had a problem...
Most coral (not all) retreat at night and open back up in the morning or when the lights come back on. I have a tongue coral, frogspawn coral and a few others that do the same thing. As long as they open and look good in the day/lights are on and your levels are in range...I wouldn't worry to...
I heard they will eat your zoas or welsos...they r cute though!!! I wanted a starry blenny, but after hearing they will eat my coral...I decided not to :(