When you say that Metroplex is alright to use with cupramine, is that only when you're feeding or does that include dosing the tank water as well?
I've been quarantining a kole eye tang for 15 days now treating with cupramine but he still has the same spots. No more, no less. He's already been through one freshwater dip and a 90 minute acriflavin dip then place in a brand new sterile tank.
That looks like Lympho to me. It's the fish equivalent of cold sores, just clean water and good foods to boost the immune system.
If you have already treated him for 15 days, it might help to move him again - without lowering copper- to another non-medicated, sterile QT. Copper is an immunosuppressant.