I've had a purple tang for about four years. He was in my 75, then my 180, then a friends 220, and finally back with me in the 300. He was the only fish in the 220 of my buddy's, which was filled with live rock and corals. I tried to catch him for nearly a year until one day he just swam into the net. Finally brought him home again. When he arrived I put him in a 30 long for about two weeks so I could observe him and let him get acclimated. Now realize I have about 9 or 10 tangs in my 300. They all get along great and I've never seen them fight at all. The purple tang is about 5 inches and when I put him in it was chaos. Even the smallest kole tang harassed him. After a day he looked like he'd been ran through a paper shredder. Fins torn off, loss of color, just sad. Well, I stayed up late waiting to catch him with the lights off, so that I could return him to my buddy's tank. This guy never slept. After two weeks of trying I gave up. He was eating really well, but still looked awful and now only a yellow tang, about half his size, would harass him to no end. Every time he came into view the yellow tang would chase him back into the rocks. Now flash ahead a month later. The purple tang now looks great. Healthy, fins all healed, and he swims around the tank with all the other fish. Except one. He now chases the yellow tang instead of the other way around. They don't fight, thank goodness, the purple just chases him around. I can tell they don't fight because the yellow has no signs of torn fins and I've never seen them back into each other as before.
I realize this post is long, but wanted to explain the behavior of tangs. The purple tang is one of the more aggressive of the tangs and can be a nuisance. That's one of the reason's I added him last. I do believe that all things are finally settling down and everyone will be happy. Realize I do have them in a 300 gallon tank, with lots of hiding places and plenty of room to swim. As you can see I'm a tang lover. By far my favorite fish. If I had it to do over there would be a black tang in there. I'm not going to put one in now though, it would be terrible to see such an expensive fish go through all that.
My two cents,
Richard