The Waterco FulFlo Tri TC400 filter cartridge is designed for compatible filtration applications where cartridge replacement is part of routine service or larger filter restoration. A filter cartridge is useful because it provides the surface area needed to trap debris and fine particulate matter as water passes through the system.This replacement is especially useful when the original cartridge is clogged beyond practical cleaning, physically damaged, or too worn to continue delivering the desired filtration performance. The note that three are required helps buyers plan a correct full replacement rather than only partially refreshing the filter set.The 622820 is a practical cartridge choice when a compatible Waterco FulFlo Tri TC400 system needs properly matched filter elements for a more complete filtration refresh. Waterco FulFlo Tri TC400 filter cartridge Designed for compatible cartridge filtration applications Helps restore dependable debris-trapping performance Useful when the original cartridge is clogged or worn out Three required for a full supported replacement set