There is little to no benefical bacteria in the tank water. It should never be re-used. A QT tank needs to have 2x/day PWCs to maintain water qualtiy until a biological filter can be established. I used a hob
with a biowheel when I had to treat for Ich, BUT I treated with what is IMO
the only safe and effective method, Hyposalinity. Since then I have kept the biowheel in the sump and have been able to use it to establish a filter whener I need to set up a QT tank for new fish.
Right now you need to be prepared to 20% PWCs twice a day until you can get some bacteria growing. Beneficial bacteria only grow on a surface (sand, rock, filter material, biowheel, etc.)
Too bad you started a Coperafe treatment. IMO
it's very hard to control the dose considering all the PWC
's you must do. I guess you can treat 2 gallons of water before adding it each time. Can you acurately dose a 1 gallon jug?