Help with ick

I need some help I've been on the hobby for about a year now I went from a 40 breeder to a 75 gallon and will go with a 200 gallon in near future. I recently got a blue tang a baby I it has been in quarantine for about 3 1/2 weeks I started the Cupermine after it was in there for about a week because all I could get my hands on at the time was ParaGard so I did that until I got the Cuprimine . my question is how long until I start seeing results that the Cupermine mean is working , tang still has the white fluffy stuff on the outside of its body . Also does Cupermine make your nitrates read higher than normal I've been doing several water changes and monitoring how much Cuprimine is in the tank my nitrates have been very high . My fish eats a few times a day active playful .