This is from Humblefish's sticky for "treatment options 102" It confirms the therapeutic levels for you.
Copper: Treats Ich (Cryptocaryon irritans), Marine Velvet disease (Amyloodinium); possibly Uronema marinum
How To Treat - First, it is important to know what kind of copper you are using. Cupramine is fully charged (ionic) copper, and has a therapeutic range of 0.35-0.5 mg/L or ppm. You would use a Seachem or Salifert copper test kit for Cupramine, as those are capable of reading copper in the low range. Coppersafe, on the other hand, is chelated copper. It has a much higher therapeutic range of 1.5-2.0 mg/L or ppm. As such, you need a “total copper test kit” such as API’s to measure Coppersafe.
Standard copper treatment lasts 30 consecutive days. The reason it takes so long is copper only targets the “free swimming stage” (the same holds true for all chemical treatments & hypo). While 7-14 days is the “norm” to reach this stage, certain strains of ich have prolonged life cycles. Indeed, even 30 days may not be long enough in some rare cases. This is why it is so important to observe after treatment ends, to ensure symptoms do not return.