I have kept several large Pomacanthus (asfur, BF, Emp, annularis, majestic) and all of them thrived and were very healthy on a mix of meaty seafood, shrimp, clam, fish, large and small Mysis, and other foods mixed in for variety, nori (almost everyday), ON form. 1 & 2, and an abundance of LR to graze from. IMO you really don't need sponge for this genus as long as they get a variety of high quality seafood and algae. I have given them sponge ON and Hikari from time to time but its more about variety. The majestic I keep now loves ON form 2, even to the exclusion of fresh seafood, go figure, but he is a toad and a very large and nice looking fish on this diet.