Cartridge filters: when to clean, how to clean, and when to replace

1Read the gauge against the clean reading

There’s no universal “clean” number: it depends on the plumbing and, on a variable-speed pump, the speed. Write the clean reading and pump speed on the filter or job card. Some manufacturers say to clean at least every 12 months, whatever the gauge says.

2Make it safe, then open up

1. Turn the pump off at the power, and turn off any timer or controller that could restart it.
2. Close the suction and return valves, where fitted.
3. Open the air bleed and wait until the gauge reads zero before you touch the lid. The system can stay under pressure after the pump stops.

Never loosen a lock ring or clamp while the pump is running or the filter is under pressure.

3Clean for what’s actually on the pleats

• Dirt: hose inside and out, working the water between the pleats, at about 45° from the top down. No pressure washer: it can damage the element.
• Oils and sunscreen: hosing may not shift them. Soak in a cartridge cleaner or degreaser for as long as the label says (anything from an hour to overnight). A spare cartridge keeps the pool filtering meanwhile.
• Calcium and mineral scale: plain acid removes scale, not oil. Degrease and rinse before any acid soak, as acid on an oily cartridge can shorten its life. For a plain acid soak, use pool acid such as AquaGUARD Hydrochloric Acid Balance 5: follow the label. Some filter cleaners do both in one soak: follow the label.
• Acid handling: add acid to water, never water to acid. Wear the PPE on the SDS: for pool acid, splash goggles with a face shield, impermeable gloves and an apron. See our SDS library.
• Biguanide pools: the wrong cleaner can turn the grey film into a gum that can’t be removed, and the cartridge then has to be replaced. Use that system’s cleaner.
• Rinse thoroughly after any soak, before the cartridge goes back in or into another product.

Never let chlorine and acid meet. Some manuals suggest a mild chlorine soak, and some filter cleaners are acid-based, including AquaGUARD Deluxe Filter Cleaner (sulphamic acid), whose SDS says never to mix it with chlorine. Rinse thoroughly between a chlorine soak and any acid cleaner, and use separate containers: chlorine and acid give off toxic gas. See WorkSafe WA’s pool and spa chemicals guidance.

Spent solution: dispose of it as the product SDS and your local water authority require.

Closing up

1. Check the lid O-ring is clean and seated.
2. Lock rings: hand-tight only where the manual says so, as overtightening can cause leaks. Clamp bands may have a set torque. Follow the manual.
3. Re-open the valves before you start the pump. Some manuals warn that starting with them shut can cause serious injury or damage.
4. Open the air bleed, stand clear and start the pump. Close the bleed once a steady stream of water comes out.

Replace, don’t clean, when…

• It’s torn, holed or damaged, or has flattened pleats, a crushed core or cracked end caps.
• The reading stays high after a proper clean. Some manufacturers say replace when a cleaned cartridge still reads about 30–40 kPa above a new one.
• Age is a guide only: some manufacturers quote about three years on average, depending on bather load, wind and dust.

Don’t floc through a cartridge

Floc may clog it. Some floc labels direct you to take the cartridge out, refit the empty housing and circulate, then let the floc settle and vacuum to waste. See cloudy pool water.

When it isn’t the cartridge

Final step

Once it’s running, write down the new clean reading and compare it with the new-cartridge figure.