Ick help

Sometimes, the best treatment for your fish is not to do anything at all and let the nature do it by itseft. Catching the fish and make him dip in FW will only stress him even more and you will make it worse. it will be good to have a cleaner shrimp that will make his station for your fish having ick. Usually, if your water is in good condition, your fish will get back healthy. Hope your tang is still small because you will need a bigger tank later on for him