[Olliereefer]

Another good cure to marine ich(whitespot)is not to stress the fish out by moving it to different tanks ,Keep your water conditions spot on and the main one is to keep your hands out the tank!
You will find that tangs usually bounch back after a week or two if the above is done.
If you have just added the tang it's almost guaranteed that it will have a case of whitspot and will from time to time for no apparent reason.
Good luck
Ollie