If you are talking about the silvery looking spots that is normal but I'm sure you are refering to something else. Sorry on a phone right now. Coppersafe is made by mardel. It is for ick, velvet, and other external parasites. Seeing I can't see the spots I can't confirm what you have but the flicking is usually a good sign of external parasites.
Silver datnoids are listed as brackish fish but can do well in full fresh also. So if you wanted to go 1-2 tablespoons per 5 gallons you can but I am not sure how the stress levels may be changing him around like that can be when you go to add him back to the main tank.