Cloudy water can be a result of an inefficient pool filter. To maintain a clean, clear pool all summer, make sure your sand pool filter is working efficiently by refreshing the pool filter sand every three to five years or sooner if you're running your filter continuously. HTH® filter sand works with all sand filters on pools and spas of all sizes. HTH® pool filter sand is the purest, most closely sized pool filter sand available thanks to a rigorous washing and grading process. Follow your filter manufacturer's recommendations for filling a new filter or for replacing sand in an existing filter.