Those white-ish areas should be viewed with great suspicion. Could be some sort of bacterial infection. Keep in mind that bacterial infections are usually the result of some other cause like parasites, injury from scrapes or aggression, etc.
Consider treating with Ruby Reef Rally in a QT or in the DT. It's very mild yet really helps the fish's immune system giving it time to recover. The manufacturer claims it is reef safe. I've never had a problem using in the DT but I don't like to treat in there.