Do you have a copper test kit? The copper treatment packaging should recomend what kind of kit to use. You want to maintain the recomended ppm
levels, not add medication per fish.
Copper is somewhat toxic to fish as well as the parasites, so you must be very careful with dosing it. Have you considered the hyposalinity treament instead?
The copper will not kill the parasite while it is on the fish, you must wait for it to naturally drop off to reproduce. The copper will kill the next generation of parasites as they are swimming around looking for a fish. All methods of ick treamtment work this way, interrupting the life cycle of the parasite rather than directly treating the fish. Most of the visible part of the ick is the fish's immune system response, not the parasite itself. How long it will take for the ick to drop off depends on exactly where in the lifecycle the parasite is. It may take some time. You want to continue the treatment for a month after the parasites fall off.