I bought a threadfin butterfly and my yellow tang was actually able to hook him with his tail barb -- right in the side. After about 5 days of costant abuse the tang let him be --- in a 72 gallon bowfront.
Now that the fish were all healthy and got along I got an ich infection Christmas day and lost my threadfin two days ago -- lost a clown last night and the coral beauty looks next if he doesn't recover. The only one that looks completely recovered is my tang.
Anyways -- the big problem I found with the threadfin is his color matched the yellow tang pretty close as the tang didn't care about other fish introduced which probably resulted in a territorial battle.
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90 gallon with 26 gallon sump/refugium, 2 x 250 MH lighting, 100lbs live rock, 1 - yellow tang,1 damsel, 1 - cleaner shrimp, 1 - coral banded shrimp, 3 - emerald crabs, 2 - porcelin crabs, 6 - peppermint shrimp, 1 - green ricordia, 1 - toadstool, 1 - brittle starfish, 1 - sand sifting star, 100's baby feather dusters,Ass mushrooms, frogspawn, xenia, 1 clam,
6 - Leather coral, Green star polyps,Lime green/orange button polyps,1 huge carpet anenome,various snails/hermit crabs | 
Butterfly RIP 
jb
