I wouldn't use it regardless. Coppert in a QT tank is best (and only way in my opinion) to cure ich. Don't bother with any products. They mask the parasite until either a) the fish dies or b) it builds up an immunity. Either way, the parasite is never out of your system.
So get some cupramine, a 10 gallon tank, a heater, a sponge filter. Put your fish in it. Keep them in it for 6-8 weeks. Treat with copper for 4 in the QT only. At the end of the 6-8 week fallow period, put the fish back in your DT.