Hard to tell what it is from pics.
If velvet (looks like powdered sugar vs the salt grain appearance of ick) you probably want to do a 5 min freshwater dip and I would use tank transfer method in air stones / small aquariums or 5 gal buckets (although can’t monitor fish as well), with 36 hour transfers, and a fresh water dip between some of the transfers.
Side note, QT is something I’ve gotten really good at using tank transfer per humblefish instructions. I used to QT with cupramine but turns out cupramine can be a challenge that kills your fish for various reasons - I was having more than 50% fatalities with cupramine and 0% so far at least with tank transfer. If you absolutely want to use copper, go with copper power because it’s more stable than cupramine. The other issue is it seems you have an acute issue, and if you use copper you won’t be able to ramp up to therapy levels before the fish die. When you tank transfer, the fish is immediately cut off from the reproducing ick/ velvet.