So, I get pool to shock ing level, clears up then maontain cl to above 3 but water still turns green within 3-4 days. This is even with out pool use ..temperature has been in upper 90 ' s to lower 100's. Pump running 12hrs a day and sand filter backwashed accordingly. Any ideas? Other than shocking, I maintain it to above 3 cl with tabs. The cya is between 40 and 45. No cc last time I checked. Pool is about 20k gallons but I round up to about 24k to be safe. Sand in filter is new. Dont brush as much as I should. But I thought the walls and floor would show that thier dirty, not the actual water. ThNks for any advice.