As for the copper, the life cycle of the parasites it cures is 14 days. So, in theory, 14 days would be sufficient. Most writers on the subject recommend 21 to 28 days. My own feeling is 21 is sufficient. The tank the fish came out of also has to be treated. If it remains empty of fish for six weeks then most everyone agrees it is a safe tank. Apparently the six weeks have to do with delayed hatching of the parasite's eggs. In addition, I have treated the tank with PraziPro and, when I get it in the mail, I will treat it with Revive. This should take care of everything. I should be getting the Revive in a few days. So the tank the fish came out of will not be safe until May 15. Fortunately, I have a 40 gal tank that should be ready for fish in a week.