Most all modern filter housings include a pressure gauge that indicates the strain under which your filter is operating. The more dirt and debris that accumulate in your system, the harder it gets for your pump to circulate water through your filter cartridge. As dirt and debris accumulates, the pressure gets higher – it’s important never to let the indicator gauge get close to “maximum.” As a general rule, once the pressure increases to 8 to 10 PSI, your cartridge should be cleaned or replaced.