Having any ammonia or nitrite will mean it's cycling. Since you have just used a copper treatment I would actually suggest you empty it, clean it with a mild bleach solution (10:1) and rinse thoroughly. Let it air dry a few days, re-fill the QT
and seed it with something from the main tank.
Not all new fish need to be treated so having the time to properly cycle the QT
first will go along way to keeping the fish healthy during it's alone time. I know it will seem pointless if you end up treating depending on what it is but it all helps.