I have had a medium sized tang (about 4") in my tank with a chromis, clownfish, and mandarin goby. At first, he would occassionally pick on my chromis *he's just the bully of the bunch*. I bought a butterfly fish (about 6") from liveaquaria.com and saw he was compatible with everything in my tank. I was worried about that being right since they look so much like tangs, so I called the company and the man assured me they got along. He said only tangs don't get along with other tangs unless they're introduced at the same time. So I spent about $50 on this butterfly fish and when I introduced him into the tank, the tang instantly made himself look larger, put down it's forehead (like a bull) and nips at my butterfly fish. The butterfly is much larger than the tang. Is this normal? And is there any possibility that the tang will lay off the butterfly after a while or I'm looking at a dead fish and a wasted $50?