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?
180G build thread
180G All-glass with dual megaflows in a custom stand
AquaC EV-180 skimmer
250 pounds LR
160 pounds aragonite
Custom acrylic sump from GlassCages.com
2xPCX-40 return pumps
2x250MH 14K, 2x175MH 14K - PFO lighting, 2x65W PC
No-name 36W UV
Water General 125GPH RO/DI