To fatten that tang up Iwould suggest some pemysis. It is fullof protein, much more than regular mysis. I would also add brine shrimp, some blooworms and some emerald entree to the mix. PLUS make sure there are seaweed sheets available as much as possible.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.