My banner fish definitely has something wrong!

[Mom.VS.Reef]

Opinions on what this could be?
He was in qt for 3 weeks and did just fine, but now that we moved him to the display tank, this appeared.

His appetite and energy is just fine.
His only symptom other than shown in the picture is on and off twitchy behaviour.

When we first got him it appeared that he may have been in a minor fight. I’m wondering if it could possibly be parasites??
Any advice it helpful. Thank you!
Black parts of his are slightly while in colour, and white parts are slight black...base of tail fin appears to be browning...


Any advice it helpful. Thank you!

 

[JumboShrimp]

I would treat with API General Cure right away, 1 packet per 10 gallons of water like the instructions say. Most U.S. pet stores carry it, or Amazon can get it to you in 2 days.