Your going to have to post more info,Sorry about that but from the pic it looks to be Ich or velvet which in that case I would Qt and start on cupramine copper.Maybe do a 5 minute fresh water dip first to give him some relief.
If you need any help my number is 585-689-3982 call me anytime! Im sorry I could not be more help but it's hard to say from the pic and without more info on fish its even harder.
Is he flashing off the rocks,labored breathing,eating at all? or just a little? when did the spots come about? what size tank ect....