In what I have read and experienced is, try not to ever dose the main tank with meds. When you medicate the main tank, you run the risk or do, kill beneficial bacteria.
Protien skimming I don't believe will take out the meds. I know it doesn't deplete the Cal content, or it hasn't in mine anyway.
If you have dosed the main tank with Copper and want to create a reef, I would do water changes as much as it takes to bring the Copper down to acceptable levels testing with a test kit for Copper. I would run High Quality AC
for a few days and change it out and then do it again to rid the tank of left over if any, meds like formalin and what not that may be in the tank still.
After that, just give it time to repair and build the bacteria back up and you should be ok to go...Hopefully the LR
is not harmed if medicated is the case. if so, it will become LR