I think I would get aggressive at this point.
Do a water change to get the copper back to the appropriate level first. Then, give another 90-minute rally bath to all of the fish and dose the QT with kanaplex + metroplex + furan-2, in addition to the copper.
You’ll want to run ALL three, together for 14 days.
The furan-2 is dosed daily. The metro/kanaplex will be dosed every 48 hours after 25% water change (make sure copper is in the bucket before it hits the tank) Dose the metroplex in the higher range - 2 scoops per 10 gallons.
Add as much water movement as possible. An airstone and a powerhead aimed directly at the surface.
This combination of treatments will cover ich, velvet, brook, uronema, and bacterial infections.
Once you’ve finished 14 days, I’d highly suggest setting up a second sterile QT (med-free) and transferring all fish from the current tank to that one.
If there are still symptoms of infection, you may need to run a more aggressive course of antibiotics in the second QT without copper. NFG is preferable, but Triple Sulfa + Furan-2 make a decent substitute if you aren’t able to get the NFG.