The purpose of a pool cartridge filter is to clean your pool water by capturing debris and contaminants in the folds of the filter. With time these folds will become clogged, water will not flow thru the filter as easily, and pressure within the filter will increase. Operationally, with water flow down, you will not be turning you pool water as frequently and your pool contaminants will start to build up. It's time to clean your filter. As a general rule of thumb, your filter should be cleaned at least once a month during the summer and every other month if your pool is operational during the winter. This guide shows you how to replace multiple cartridges in a large Jandy CL580 Cartridge Filter. Although this guide is specific to the Jandy CL580 Cartridge Filter, many steps are common to other models of large cartridge filters.