White spots on my Tomini Tang??

[newreefer_59]

I have had a Tomini Tang for about a year now (about 3") and has recently developed white spots on much of his body and fins. Have 15 other fish with nothing and all look and feed fine. I am thinking it must ne ich or some such parasite, but why it occer now? Have a 150 reef/fish tank that is otherwise healthy. Is there anything I can do? pics were not possible as he darts around very quickly and is camera shy.