The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
Powder blue tangs like all tangs are very sensitive to water quality, (scaleless fish) if your tank has any signs of inperfections of water quality your powder blue will most likely stress out, causing ich.
Make sure your tank is established and you have a UV sterilizer!