A couple of days ago I noticed that my 4" blue tang is nipping on my sps corals. What causes that behavior? I feed my fish, including the tang, twice a day with different types of food (also using dry algae for my angel dwarf and the tang). My h20 parameters are 0 ammonia, 0 nitrites, 10 nitrates, S.G. 1.023. Water changes are performed every week and a half 15 gallons for a 55 gallons tank. Thanks for any help.