When you add the Polyquat, you'll want to have your filter on recirculate instead of filter or else you'll just filter it all out. Also, the Polyquat will drop the chlorine level, so a day or two later, you'll need to add more chlorine to bring it back up. You don't want to cover a pool at shock level as the fumes can damage the cover. Give it a couple of day or two after shocking before putting the cover on for the winter.