I have a Powder Blue, Achilles, Blue Hippo, Purple and Whitetail Bristletooth currently. They were all added at the same time, (except for the Bristletooth) and the Achilles and Purple were the two that decided to go to war with each other. I tried separating the Purple since he was winning the battle, but upon return he almost killed my Achilles so I took the Achilles out and put him in another tank to heal. The plan was to sell him when he fully healed, but that did not happen. A few weeks later I decided to give it another try and the Achilles and Purple have gotten along ever since. Although my Achilles did kill my Harlequin Tusk. :(
I recently added my Whitetail Bristletooth, (a little over a week ago) and tried a large acclimation box, but none of the others paid any attention to him or the box at all and I felt bad having it in a box so I let it out after only 24 hours. The Purple almost immediately let it know who the boss was, but didn't do much damage besides a torn top fin. Surprisingly the Hippo was the main bad guy, but they only went at it for about a day and a half and then they decided to get along. The Whitetail is now swimming all around with the other Tangs with no issues besides the occasional flared fins and squaring off without actually doing any tail slapping.
That all being said...they main way I keep piece in my tank with so many Tangs is to OVER FEED the heck out of them. They keep getting food in the morning until they stop eating, (which is a lot) and they get fed again in the afternoon, (seaweed on clips) and then again in the evening. I have a slightly over sized protein skimmer and a large UV Sterilizer and have not had any issue with higher Nitrate, Phosphate or algae since I started doing this so. I have found that a fat Tang is a happy and less aggressive Tang. ;Happy