If you own a reef, then you can't put any treatment in there even something that claims for reefsafe, better be safe than sorry.
Most tangs are prone to ick. Stress free environment would help tangs become immune to ick. you have a 58g tank which is too small to get more than one tang in there. They would probably fight for territory. I did nothing when my fish got ick because it would be gone as long as the fish were not under stress, eating well and water quality was good. Powder Blue and Blue tangs are more prone to ick than yellow or safin tang. So pray now! Good luck to your tangs.