Raising the temp is a freshwater trick. It does not do anything for saltwater Ich. Some say that garlic additives increases the immune system. That can't hurt to try. You don't want to treat your DT with copper or hypo, so if QT is not an option, then you've got to just keep parameters as pristine as possible and hope that the fish can tough it out. Some will, so Ich is not always a death sentence (like some other things are). Without doing the fallow tank, Ich will likely survive in the DT and you run the risk of it coming back in the future.