i have a 15ft above ground pool and this year i have drained it twice as the bottom of the pool keeps going dirty and when i scrub it the water turns greenish i am using 20g multi tablets and also chlorine, all levels are as they should be when i test water. i was told to shock the pool every time this apears by the people i got the chemicals off but still there i even added some algaecide to see if that helped and still the same so i begging for any advice as kids are desperate to use it