Zebrasoma tangs, the yellow & purple, really don't like each other. Its a typical "individual fish'' thing, but (IMO & IME) these two could really go to war and I think a 120 is borderline size for the two. Zebrasoma tangs often do better when there are 3+; but just two is often impossible. It may work, may not---have a plan to remove one if you need to. I think a standard 120 is only 4' long and this adds to the potential aggression problems.