Because of the sand in the filter tank main pool started out life. The number 4 cylinder, filter nam SA bad causes cloudy water in the pool start to complete the pool filter sand should be changed.
The sand in the filter element from an end-of-4 with a bucket of water. Swimming in the pool made a poor start to filter turbid water should completely replace the sand.
Because the sand filter main start end of life of 4 pool tank has a water filter. Outdoor bad water pond glassy to filter pond complete should change the sand.