I really feel that tangs are ick magnets,I have taken the approach of not qt the rest of my tank,only the ones that are breathing heavily and need special attention. I am just using hypo on the other fishes that are really covered with white spots but the rest of my display,been feeding them ocean nutrition seaweed with garlic,they love it. My tangs and wrasses go crazy at least three times a day on each sheet by 3 inch by 2 inch on a veggie clip. I am also discovering that my salinity was a bit high,another reason they were stressed,bought a refractometer today and discovered it was at .030,wow. So I had to lower it slowly to .027 and my goal is to reach .024 and .025 by next week,asked vivid aquarium about it and they stated that it may be a contributing factor and a good reason too that salinity should be lower so I could save on salt on a big system at 305 gallon total water volume. I also felt that everything was not in place in this latest upgrade from a 125 to a 225,my biological filtration was not up to par so I hope to fix the problem with a 58 gallon I turned into a plenum/refugium to stabilize the whole tank. I hope that ick will go away and I have a few more weeks left on its cycle which is 8 weeks,giving it two just to make sure no one else gets sick because ick will be still on the rocks and sand. So far the blue,sailfin and yellow tang are recovering with less spots everyday,gladly that wrasses are not ick magnets,also running uv sterilizer to cut the cycle down of the disease and hoping that increasing water quality will help cure everyone.