Need Help With Sailfin tang URGENT

[TaioneReefer]

Hey guys,

So I recently decided to treat all my fish with copper as my naso tang caught it and died.

Now I woke up seeing this sailfin tang laying and breathing really fast.
it was fine, with no ich and all, but just decided to treat it anyways so later on there wont be another ich breakout.

first thing i noticed was : colour fade on the black bars, and now its looking like this :


anyone know why its getting worse after treatment? (treating with cupramine) at 0.5 tested with seachem test kit

please give me some input.

Thanks