This past Sat. I purchased 3 yellow tangs for my 125 FO. They seemed to pal around for a little while, but then one started hitting the others with his rear fin. Now four days later only one of the tangs is swimming around and I occasionaly see the other two swimming through the maze of rockwork, occasionally comming out but for no longer than a minute at the longest. Is this something to worry about? Should the bully be taken out and replaced? I also thought about adding two more to make it more of a group. Suggestions?