The Cartridge filter CF23 is for filtering pool water. It is important to take care of water hygiene in pools. And the physical part can be taken care with a cartridge filter. This filter is based on using a fiber based cartridge for filtering the pool water. It works by the pump moving the water through the cartridge walls from outside to inside. It can be used in small swimming pools and hot tubs. On top of physical filtering it is important to use chemicals in the water to keep bacteria and viruses under control.