A great choice! 8) Holocanthus passer is one of my favorite angels. They are aggressive, and problems my increase as he get's larger. (in your situation, groupers in particular can be victimized) However they don't grow very fast, which is both good and annoying. Good because a juvenile can be acquired and housed in smaller quarters (realatively speaking) for quite a long time. Annoying, becaue the adult coloration is GORGEOUS, but rarely seen in captivity. It takes forever and a day for them to change, as they have a rather protracted juvi coloration stage. A 6" passer still does not have the adult colors. :?
Males end up with white pelvic fins.
Good luck
Jim