How to Clean a Cartridge Pool Filter

Cartridge filters are the low-maintenance choice of the three main filter types, but "low-maintenance" doesn't mean "no maintenance." A cartridge that's never had a real cleaning slowly loses filtering capacity, your pump works harder to push water through it, and your water clarity suffers even though the chemistry looks fine on paper. The good news is that cleaning one properly takes about thirty minutes of hands-on time, plus a soak that happens while you're doing something else entirely.

How to tell it's time to clean the filter

Cartridge filters tell you when they need attention, if you know where to look. The filter pressure gauge is the most reliable signal: note the pressure right after a fresh cleaning (this is your baseline), and plan to clean again when the gauge climbs 8 to 10 PSI above that number. Reduced water flow from the returns, a pump that seems to be working harder than usual, or visibly cloudy water despite normal chlorine and pH readings are the other common tells.

• Rising filter pressure: the single most reliable signal, tracked against your post-cleaning baseline.
• Weaker return jets or noticeably slower flow at the pool's return fittings.
• Cloudy or hazy water that doesn't clear up after normal chemical dosing.
• It's been roughly 3 to 4 months since the last real cleaning, even if nothing looks obviously wrong yet.

Step 1: Rinse before you soak

Turn off the pump, relieve pressure from the filter tank (most have a small air-relief valve on top), and open the housing. Pull the cartridge element out and hose it down from top to bottom, working the water into the pleats at an angle rather than straight on. A garden hose nozzle with a decent fan spray works fine; you don't need a pressure washer, and a pressure washer used carelessly can actually tear the pleat fabric. Spend a few minutes here fanning out each pleat gap so you're not just cleaning the surface.

Step 2: Degrease if the cartridge has an oily film

If the pleats feel slick or greasy after rinsing, that's usually sunscreen and body oil buildup, and plain water won't fully remove it. A dedicated pool filter degreaser or cartridge cleaner solution, mixed per the product label and used as a soak for 15 minutes to a few hours, handles this well. Some pool owners use a diluted dish soap solution for light oil films, but a purpose-made filter cleaner is more reliable and less likely to leave residue in the pleats.

Step 3: The muriatic acid soak

This is the step that actually restores lost filtering capacity, because it dissolves the calcium and mineral scale that plain rinsing can't touch. Muriatic acid is a strong acid, so treat this step with real care: work outdoors, wear gloves and eye protection, and always add acid to water, never water to acid, to avoid a violent reaction. A commonly used ratio is roughly 1 part muriatic acid to 10 parts water in a plastic bucket large enough to fully submerge the cartridge, though you should follow the ratio on your specific product's label since concentrations vary.

• Submerge the rinsed, degreased cartridge fully in the diluted acid solution.
• Watch for fizzing, which is the acid reacting with mineral scale, that's the solution working as intended.
• Soak for about 15 to 30 minutes; check the label on your product, since concentrations vary by brand.
• Lift and lower the cartridge a few times during the soak to help the solution reach between pleats.
• Rinse thoroughly with a hose afterward until no acid smell remains, then let it drain and air dry before reinstalling.

How often to do each type of cleaning

When to replace instead of clean

A cartridge that's torn, has pleats fused together with hardened scale that survives an acid soak, or that no longer restores your baseline filter pressure after a proper cleaning has reached the end of its useful life. Most cartridges hold up for two to five seasons with regular care, less in pools with heavy bather load or minimal maintenance. If you're tracking filter pressure over time, a cartridge that needs cleaning more and more frequently just to hit the same baseline is usually telling you it's time to replace rather than clean again. Logging each cleaning date and the pressure reading before and after, which Skimmer does automatically as part of its equipment tracking, makes that trend obvious instead of something you have to remember.