Ok, unfortunately neither one of those 2 products has enough green matter for the fish alone. It may be getting some from the rocks but keep in mind that these fish are herbivores, mysis shrimp is not a natural part of there diet, and if fed primarily with mysis and formula one this fish is very susceptible to disease like it appears to have picked up.
I have a yellow tang, and yes he does occasionally eat mysis and flakes and pellets (etc.) but he also has 2 clips full of dried seaweed per day that hang on the tank full of nori (dried seaweed) for him to graze on as well as algae off of rocks and powerheads and what not.
The problem may simply be that the fish is not getting enough greens.
Hope this helps,
Jay