I have 6 zebrasoma's (5 yellows and a gem). I had a purple with them also but when I added the gem, the purple became aggressive toward the gem. Not the yellows, just the Gem. So the purple had to go. But the purple and yellows were together for several years though and got along fine. It was zebrasoma #7 that did it. Although purples are known for becoming aggressive as they get older too. So can't say if it was his age or too many zebrasomas that caused him to flip. He was pretty big.
I also have a mated pair of Naso's, an Achilles, and a Hippo.
I have a Fowleri and a white tail bristle tooth in the acclimation box right now also but they haven't been released yet. This will be my first experience with 2 acantharus together (Achilles and Fowleri) so I may pull the Achilles out for a couple weeks while I introduce the Fowleri. The Achilles thinks he owns the tank, even though he is one of the smaller tangs in there. Fowleris are EXTREMEY timid and the Achilles could give him a nervous breakdown. But that will be a total of 12 tangs in my tank.
I think size of your tank is the biggest advantage to keeping multiple tangs. They tend to get on each others nerves and swimming room helps reduce that. Tangs are very active swimmers and need space. Most of my yellows I added when they were small and added at the same time so they have grown up together. But I believe space is an issue because when I had the 5 small yellows in a 40g QT for 2 months, they fought. Once they were added to the 400g, the aggression mostly stopped and they were best friends.
I also feed a lot of Nori daily as they say that helps with aggression. I use 3 separate clips so they aren't all fighting over 1.
