Mimic Tang Sick?

[Ammirati]

Hello everyone - Newbie here of about 6 months. Hopefully I'm posting this in the right spot. I learned the hard way to quarantine every! Ick wiped out my DT and it's been sitting fallow now for just over 40 days so a little over halfway to the 76. I have 2 quarantine tanks right now and they are 12 days in Coppersafe so far. Everyone is looking awesome except for my yellow mimic tang. His head is turning brownish. I know they don't stay the bright yellow but the brown color doesn't look normal. He's eating great and swimming normal. My Ammonia and nitrites are zero, pH 8.2 and nitrates 5. The coppersafe is a little over 3...it was over 4!!! I know way over what it should be. I didn't know it was so bad because the api color chart is so hard to tell so I bought a Hanna HR Copper tester. I got the level down but obviously I have to drop it to 1.75-2 ASAP. Everyone else is looking awesome. Is this a disease? Hopefully you can make out the pic not easy to photograph a fish who keeps moving. Thank you for the advice in advance!

 

[MERKEY]

Could be a couple different things...I would think you would start treating with metro or prazipro or API General cure but let's see what the pros say.

@Humblefish
@HotRocks
@4FordFamily

 

[Big G]

Many fish "show" their "upset, angry, not happy" colors in QT. My Foxface looked almost black while in QT. Took awhile once it was placed into the DT for the bright yellow to return.
So if it is eating, swimming, and breathing normal just keep an eye on it.