People may wonder why their water is crystal clear one day and 2 days later it is going green… This is not always chemically related. It could be that your filter needs to be cleaned, could be a sand change is needed, or your filter is not running long enough or not at all. Sand change is recommended every 4-5 years and a filter clean is to be done twice a year. And if you have the same water for over 6 years it could be that your entire pool water needs to be drained and refilled. After 5-6 years your pool water may just stop responding to chemicals. In any case have a pool technician come out and check your entire system out and give you some insight.