My thoughts on ich on marine fish is that in many cases, if the tank is healthy and the fish are well-fed and not stressed, the fish will fight this off on their own. When I got my first tangs (a sailfin and a
blue tang) 8 years or so ago, they developed ich within days of putting them in my tank. Quite a few spots, but not immediately life-threatening, it seemed. The spots came and went, and came again, as the parasites went through their life cycles. I worried quite a bit, and after a week or so talked to the wholesaler I got the fish from (this was a pretty cool guy who seemed to really know his fish and cared a lot about the health of the fish at his facility (unlike some other wholesalers who will remain unnamed)). His basic response was that if it had not killed the fish yet, it was unlikely to do so, and that usually the fish will just fight off ich on their own. The stress of a quarantine tanak and treatment might be worse than just leaving the fish alone.
For whatever its worth, this is the approach I have taken whenever my marine fish have gotten white spots, and in all cases so far the outbreaks have subsided on their own. If the fish get stressed (e.g., temperature stress or something), sometimes the blue tang in the 220 will get some spots, and this might spread to the other tangs, and occassionally the purple tang has gotten a few spots in my main reef in the lab, but these outbreaks have been rare.
Feeding the fish really really well with very nutritious foods will probably help a lot as well.
Your results may vary.
My main point is that you might not really have need for panic (assuming this is ich).
A cleaner shrimp might help a lot as well.
