How Often Should You Replace a Filter Cartridge?

The honest short answer is one to two years. But if you want to get it right instead of roughly right, the calendar is the wrong thing to watch. A cartridge doesn’t wear out on a schedule. It wears out based on how much water it has pushed through and how well you’ve kept it clean, and your filter has a gauge that tells you exactly where it stands.

The pressure rule

When a filter cartridge is brand new and clean, note the pressure your system runs at. That’s your baseline. As the cartridge traps debris, pressure climbs. Once the gauge reads about 8 to 10 psi over that clean starting number, the cartridge is loaded up and it’s time to clean it. Rinse it, and the pressure should drop back near baseline.

Here’s the part that answers the replacement question: eventually a cleaning stops bringing the pressure down. You rinse, you soak, and the gauge still sits high. That’s the media telling you it’s full of the fine stuff that won’t rinse out anymore. When cleaning no longer restores the pressure, the cartridge is done, whether it’s eight months old or three years old.

Why spa cartridges wear faster

A hot tub is a small body of very warm water with a lot of people oils and lotions in it, filtered by a small cartridge running many times a day. That’s hard duty. Most spa owners get 12 to 24 months out of a cartridge, but the spread inside that range is huge and comes down almost entirely to use. A two-person tub soaked on weekends will outlast a daily-use tub with a full crowd by a wide margin.

Size matters too. A small cartridge has less media, so it fills up faster. A 25 square foot spa filter is doing the same job as a 50, at twice the speed, and it ages accordingly. If your tub takes a little cartridge, plan on replacing it more often and don’t be surprised.

Pool cartridges and the four-at-a-time rule

Pool cartridges generally last longer than spa ones, often 18 months to a couple of years for the bigger sizes, because there’s more media and the water is cooler and cleaner. The pressure rule is the same.

The one thing pool owners get wrong is the multi-cartridge filter. A lot of the bigger systems, the Pentair Clean and Clear Plus, the Hayward SwimClear, the Jandy CV, hold four cartridges at once. In the set of pool systems I track, 14 of the 42 run four cartridges. When one of those is dirty, all four are, and you replace the whole set together. Drop a single fresh cartridge in next to three tired ones and the new one carries most of the flow, works too hard, and wears out early. It’s a false economy.

The other signs it’s time

Pressure is the main signal, but the cartridge itself will tell you things too. Replace it when the pleats are torn or the media has started to channel and pull apart, when the seams are stained a permanent brown that no soak touches, or when the end caps have gone brittle and cracked. Any one of those means a new cartridge regardless of what the gauge says.

Good cleaning is what stretches a cartridge to the long end of its life. If you’re replacing filters more often than you’d like, the culprit is usually cleaning technique, not the cartridge. Here’s how to clean one properly.

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