So to see if I am not losing chlorine overnight would I test at sunset or after, skip the addition of chlorine, and see if it goes down before sunrise? When I have added at sunset or night, it has always been higher the next morning. If I find I am losing more that 1 ppm, are you saying I need to get it to shock levels during the night - as tested in morning? I did that two weeks ago to get rid of a green pool. Added enough bleach each night for FC to be 18-22ppm the next morning. Pool cleared in 3 days and I let it drop back down to best guess chart.