In the past, I added a copper band butterfly to my tank which already had 4 tangs. The tangs were bumping and harassing the butterfly for a few days (I think about a week). I felt that the tangs were just trying to show dominance and "put the butterfly in it's place" and "squabbles" like this will probably happen in nature, so as worried as I was, I decided to leave it alone. The harassing did stop after about a week and the butterfly was getting along with all the other fish afterwards. The butterfly was living happily in my tank for about 4 months. Unfortunately, recently, the butterfly stopped eating (still don't know why?) and eventually died :(
John