purple tang has ich now :(

[mystery_reef]

i am starting this thread because today i noticed my purple tang which i have had for about 7 months now scratching himself against the rocks. he has several ich spots. all of the other fish look fine. i feed them all a very good variety of foods and greens. i have 3 green chrom. a clarki clown, metallic rabbit, a scotts fairy, lineatus and labouti fairy wrasses. those are the only fish. all in a 125 reef that has been running for over 1and1/2 years now with most of the stuff from smaller tanks. i dont know why but i have never in my 5 years in the hobby had success with any tangs until this purple which now has some ich. not sure why or what to do everything is perfect, parameters, corals, etc... it would be impossible to catch him for a freshwater dip and probably cause more stress than good. not sure whats up with him but i dont want him to die or for it to spread to the other fish especially the very expensive fairy wrasse. any advice???