It may be too late for advice, since I have already done what I am going to explain, but I wanted some feedback just the same.
My yellow tang developed popeye about two days after purchase from PetCo (I know, I know . . . I told myself I was rescuing her)
I called PetCo, and they said since I had several inverts, and several live coral in the tank, and did not have a hospital tank, that I should use Myacin (sp?)
I have been placing 2 tablets in the tank every 24 hours for four days.
The good news - Linda (that is the yellow tangs name) is looking much better. The swelling has gone down by half, and she is eating and swimming and seems happy. Also, all of the inverts and stars are fine, too.
Odd news - Bubble Coral and Octacoral. The bubble coral is completely closed, and has been for two days. The Octacoral only opens up about 25% and only for a few hours each day. I also have a meat coral, that seems completely un-effected.
I am assuming it is because they don't like the Myacin in the water. Also, I had to shut off my protien skimmer. It was removing about 2 quarts of crystal clear water every hour or so.