My tang wouldn't stop chasing my parrotfish after I added him (the parrotfish).
Lucky for the parrotfish, I had to put the tang in QT for a week to treat for black spots. When I put him back in, he was much less aggressive towards the parrotfish, but instead now, just follows him everywhere like a little brother would. Once in awhile he'll flash his tail against him, especially if the parrotfish is lying down in his hiding space, but for the most part they get along well now.
Just my two cents, from a relative n00b, but maybe consider putting the tang in QT for awhile, so when you re-introduce him to the main tank, HE's the new guy.
Anyone else use this method when a non-agressive fish is showing agression?