I have the same problem. I have owned an above ground 33' round pool for a year. Everytime I got it blue, it would turn green in 2 days.Spent hundreds in pool chemicals. I finally, finally...changed the pool sand and added a sand cleaner. Pool was blue and stayed that way. I was very diligent on testing,chlorine levels ect. I live in south GA.

Over the winter my electric line was cut. No pump for a week.Pool was greener that green. Took me a week with chemicals no my pool is blue. BUT, My filter is still blowing out green. I changed the sand twice! The green is not as dark as it was, but it is noticable. It will blow out green for a second then blue. I use both the backwash and rince cycles. I have been putting a hose when I 1st start the filter back up, in front of the blow out to get rid of the green. I put CYA last season, I think I need to put some more.

Pool hold aprox 25,000 gallons water and pump takes 4- 50lb bags.

Does anyone have any other ideas?

Thanks,

Lisa