You shouldn't be adding anything to top off water. CP or any other medicine.
Back at you again this time it’s a two part question
1. With copper don’t you have to keep it at the right treatment level at all time so won’t tapping off with only Ro dilute the strength of the copper.
2. If so can I pre mix a gallon of copper at the correct dose for a gallon and use that to top off when need ? (Knowing the amount of water that evaporated )