HTH Pool Care D.E. Filter Aid 10lb. Even with regular cleaning, storms or heavy use can take a toll on your pool water. HTH® Pool Care D.E. Filter Aid helps maintain amazingly blue water by keeping your D.E. pool filter working at maximum performance. D.E. stands for diatomaceous earth, a filter media that traps even the smallest particles and debris (as much as 20 times smaller than sand or cartridge filters or 2-6 micron particles) and restores filter efficiency. This product is great for all swimming pools that use D.E. sand filters, including salt water systems.