The swimming pool filter is used for water purification, and there are three main types to choose from: Diatomaceous earth (DE), sand, and cartridge filters. The cartridge filters at Pool Express are able to remove particulate down to about 8-10 microns in size. A cartridge filter’s efficiency is measured by its micron rating, meaning how many microns can pass through the filter. A micron is a unit of length equal to one millionth of a meter (1/1,000,000 m), or 0.0000394 of an inch.Unlike sand and DE pool filters, cartridge swimming pool filters do not require backwashing, a process that can waste a large amount of water and energy. Filters that use a cartridge media trap dirt and debris that pass through the skimmer basket and the hair and lint pot. The filter is ultimately responsible for crystal clear water.