When my 220 was a FOWLR I had 5 tangs. A yellow, a Hippo, Naso, Kole and Vlamingi. Lots of people told me I was asking for trouble and I dismissed them saying they all got along great and at the time they did. Then after a few months of peace and harmony all He"" broke loose! They ganged up on the Kole Tang and beat him so bad I had to nurse him back to health in the sump and give him away. Next, they ganged up on the Valmingi. (don't know if I spelled it right). Anyway, point is, if 5 were too many in a 220 I think you're asking for trouble with 4 in a 72.