Do you mean lipofen? the drug that is used to reduce cholesterol?
In any case, please read the ich stickies on this forum. The only treatments that work are copper, hyposalinity, and tank transfer. Nothing else (including the so-called reef-safe medications) work.
Your system and fish still have ich. The reason you don't see it is because the fish are healthy enough to keep infestations in the gills only. They are, however, still stressed out from gill infections. You need to cure ich with the right treatments, otherwise this is going to continue.
Your powder blue tang does not have a skin problem. That is the stress mark that tangs get when they are under stress from either bad acclimations or parasites. From the photo, your powder blue is under a lot of stress. The first step to resolve that is to actually cure ich.