HTH Pool Care D.E. Filter Aid 24lb. 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.