Theres been very few days that no one has been in the pool. Its been 2-3 months since I have covered it. The other day was the first time covered. It wasnt a very sunny day and no one had been in it. I think it dropped 1 or 2ppm in 11 hours. If I remember correctly it has dropped uncovered full sun with no one in it. Its yo yoing too much based on replies. Just last night it was 9ppm covered and this mourning 8. No one in it yesterday except 2 frogs. the kids get out to go pee and so does the dog. It does drop sharply when we are all swimming. I would have to put bleach in it all day to maintain 10ppm