Soak it, don't blast it.

Use a garden hose with a gentle nozzle, not a pressure washer. Spray between the pleats from both sides until the water runs fairly clear. Then soak the cartridge in a filter cleaner solution for a few hours—follow the bottle directions. Rinse again and let it dry completely (in the shade) before putting it back in. That’s it.

You don’t need to replace the cartridge every time. Most cartridges last 3–5 seasons if you clean them properly. The mistake people make is either skipping the soak or using too much pressure. High-pressure water shreds the fabric over time. A low-pressure rinse and a good soak is the way.

One more thing: don’t try to scrub it with a brush. You’ll just push dirt deeper into the pleats. Water and chemistry do the work.