In my 120 I have had a sailfin tang for a few weeks and he has been hard to find, often hiding in the very back of the tank. Today I added 20lbs of rock and made some more caves and now the tang seems much more happy and comes up to the front of the tank while I'm sitting near it. Just a behavior thing I noticed and thought might help someone else new to the hobby. I also added a school of 6 one inch green chromis fish today, perhaps this also played some role as these are brave little fish.