I just went through this in my tank with a fairy wrasse that developed it all the rest of the fish seemed healthy and all I did was feed heavy and put some vitamins in the food and it seems to have subsided. I think most guys would say that whenever you put a new tang in the tank you going to develop it Especially if it came from Petco every fish I've ever purchased from any Petco eventually developed dick. Really beautiful fish though That was a nice find. The guys up in AO in Avenell also told me about some medicated food for ich you might want to try that. Good luck
I'm sorry to hear about your losses Paul.
Our SPS are just recovering from all of the issues we have had, but I am sure we can cut a few frags for you in the near future. Let us know when is a good time.