Late afternoon I tested it and it dropped below 20, so I added 4 gallons of 12% bleach in the hopes that will raise it enough to get through the day above 20 so then I can test it tomorrow night and the next morning and know that it is still above shock level. I wasn't sure how long from when I add the chlorine that it would register when tested. Maybe it would be ok to test tonight after all? I was more concerned with keeping it above shock level with this hot weather we are having for a few days. Is that right thinking? I figured it couldn't hurt to keep it up for one more day?