Pool Filter Cleaning Guide: Sand, Cartridge, and D.E. Filters Explained
Proper pool filter cleaning is the most critical maintenance task for ensuring safe, hygienic, and crystal-clear swimming water. Your pool filter acts as the kidneys of your entire aquatic system, tirelessly trapping dirt, body oils, pollen, and microscopic algae spores. However, as the filter media becomes saturated with this debris, water flow restricts, and clarity plummets. Because the three main types of filters—Sand, Cartridge, and Diatomaceous Earth (D.E.)—operate completely differently, they require highly specific cleaning methods to prevent irreversible damage.
How Do I Know It Is Time for a Pool Filter Cleaning?
You should never rely strictly on a calendar to decide when to clean your filter. The only foolproof indicator is the pressure gauge located on top of the filter tank. When the gauge reads 8 to 10 PSI (pounds per square inch) higher than the normal, clean operating pressure, it is time for a cleaning. If the clean pressure is 15 PSI, you must clean it when it hits 23 to 25 PSI.
1. Cleaning a Sand Filter
Sand filters use a large tank filled with specialized silica sand or glass media to trap particles as small as 20 microns. They are the easiest to maintain because they are cleaned via a mechanical reversal of water flow called backwashing.
The Backwashing Process
- Always turn the pool pump OFF before changing the valve setting.
- Press down on the multiport valve handle and rotate it to the ‘Backwash’ position.
- Roll out your waste hose to an appropriate drainage area.
- Turn the pump ON. Watch the small glass observation vial (sight glass). The water will initially run dark and cloudy.
- Run the pump for 3 to 5 minutes until the water in the sight glass runs completely clear.
- Turn the pump OFF. Move the valve to the ‘Rinse’ position. Run the pump for 1 minute. This resets the sand bed so dirty water doesn’t blast back into the pool.
- Turn the pump OFF, return the valve to ‘Filter’, and restart the system.
2. Cleaning a Cartridge Filter
Cartridge filters contain pleated polyester fabric wrapped around a cylindrical core. They can capture ultra-fine particles (down to 10 microns) and operate at very low pressure. Because they do not have a multiport valve, they cannot be backwashed. They require manual removal and washing.
The Manual Rinsing Process
- Turn off the pump and open the air relief valve on top of the tank to depressurize the system.
- Remove the tank lid clamp and pull out the filter cartridges.
- Using a standard garden hose with a spray nozzle, spray the cartridges thoroughly from top to bottom, aiming into the pleats at a 45-degree angle.
- NEVER use a high-pressure power washer. The extreme pressure will tear the microscopic pores in the fabric, ruining the filter instantly.
- If the cartridges are coated in oily residue (sunscreen or body oils), soak them overnight in a dedicated filter cleaner solution or a mixture of water and trisodium phosphate (TSP).
3. Cleaning a D.E. (Diatomaceous Earth) Filter
D.E. filters offer the absolute highest level of water polishing, capturing microscopic particles down to 3 microns. They utilize internal grids coated in a white, chalky powder made from fossilized diatoms. Cleaning them involves a combination of backwashing and manual teardowns.
Backwashing and Recharging D.E.
- Like a sand filter, you backwash a D.E. filter when the pressure rises 8-10 PSI. Follow the same backwash-then-rinse steps on the multiport valve.
- CRITICAL STEP: Backwashing flushes the dirty D.E. powder out of the system. You must immediately replace it.
- Return the valve to ‘Filter’ and turn the pump on.
- Mix the manufacturer-recommended amount of fresh D.E. powder into a bucket of water to create a slurry.
- Slowly pour this slurry directly into your pool skimmer while the pump is running. The powder will travel to the tank and recoat the internal grids evenly.
Annual Deep Cleaning
Regardless of the filter type, a deep chemical clean is required at least once a year (usually at the end of the season or during spring opening). Backwashing only removes physical dirt; it does not remove the sticky calcium scale or deep-set organic oils that slowly choke the media over time.
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