How Does an Inground Pool Filter Work?

Sand Filters

• Sand filters for inground swimming pools use No. 20 silica sand to filter and trap dirt particles from the pool water. As the water flows through the pump, the dirt particles are captured in the coarse sand before the water returns to the pool. Sand filters will capture dirt particles 20 to 40 microns in size.

DE Filters

• Diatomaceous earth (DE) filters will capture dirt particles from the water as small as 2 to 5 microns. The DE grid is coated with diatomaceous earth powder that works like the sand filter to trap the dirt particles. As the water flows into the pump, the particles pass through the grid, where the DE powder traps the particles.

Cartridge Filters

• Cartridge filters have a large surface for capturing dirt particles in the water. These filters function at a lower pressure when running compared to a sand filter, which means there is less back-pressure on the inground pool pump, so the pump has a higher flow of water. Cartridge filters will trap dirt particles as small as 10 to 15 microns.

Cleaning Procedure

• The cartridge filter should be cleaned once or twice during the season that the inground pool is in use. Cartridges can be removed from the pool pump and rinsed off, or hosed off while still in place, but you will need to open the drain hole on the bottom of the pump. Sand and DE filters are "backwashed" when the pressure gauge reads 5 to 8 pounds per square inch (psi) above the "clean" reading. Pool owners need to set the valve handle to the "backwash" position. DE filters are recharged with diatomaceous earth powder after backwashing. The pool owner adds the powder to the skimmer after the pump has been backwashed.