I have a Sail Fin, great fish, gets a long with all other tank mates. Only problem I ever had was with him and a mirror

I introduced a Black Tang into the mix and the 3 Yellow Tangs didn’t like it…..So I tried putting a mirror to distract them. All other fish hid while the Sail Fin went back and forth and his yellow turned purple. From what I have read is, only one per tank, regardless if it’s a Desjardinii or just a regular Sail Fin. The Desjardinii are very nice, if I could have found one I would have gone with the Desjardinii .