I too have a yellow tang in an established tank. He bullied the heck out of a foxface rabbit fish. Yellow and kinda looked like him. Still picks on him from time to time when they're trying to hide in the same place.
Anyway, I've got a yellow-eyed kole in QT
now, and the plan is to remove the yellow to QT
, return the foxface to the LFS
, change the rock work, and let the kole establish himself, and add the yellow back 2 weeks or so later. I'm hoping that the yellow will be nice when he gets back 'cause it ain't his familiar territory anymore. I've heard this may work. That may be your best bet.
Got another tank to let the yellow "chill" for a bit?