To be honest, I've never liked dosing cupramine as strongly as suggested on the bottle. IMO
/IME .5mg/l is an awfully high dosage for fish to withstand that are already unhealthy to begin with. I've lost several fish in QT at that high dosage that were showing no signs of ich and eating well. After reading the article below and discussing with other reefers, I've had much better success when dosing slowly over 3-4 days to reach an ending concentration of .3mg/L.
Take a look here for more info:
FA165/FA165: Use of Copper in Marine Aquaculture and Aquarium Systems