Can You Backwash a Cartridge Pool Filter? What to Do Instead
Cartridge filters cannot be backwashed. This guide explains why, what backwashing does to a cartridge, and the correct 3-step cleaning procedure that replaces it.
The Short Answer
No - cartridge filters cannot be backwashed. There is no backwash valve on a cartridge filter, no backwash port, and no backwash setting. The cleaning procedure for a cartridge filter is completely different from the backwash process used on sand and DE filters.
This is one of the most common points of confusion for pool owners switching from a sand or DE filter to a cartridge system. Sand and DE filters have a multiport valve with 6-8 positions including BACKWASH. Cartridge filters use a simple 2-way valve - on or off. The concept of backwashing simply does not apply.
The confusion also arises because pool care advice is often written generically. Instructions that say “backwash your filter when pressure rises” are correct for sand and DE filters but completely wrong for cartridge filters. If you have a cartridge filter, ignore every piece of advice about backwashing - the process your filter needs is different from the ground up.
Why Cartridge Filters Cannot Be Backwashed
Understanding why helps you maintain the filter correctly and spot bad advice before it costs you a cartridge element.
Sand filters work by reversal. When you backwash a sand filter, you reverse the water flow through the filter tank. Water enters from the bottom, flows upward through the sand bed, and carries loosely-held debris out through the waste port. Sand grains are dense and heavy - they tumble, clean, and resettle when the flow is reversed. Backwashing works because sand’s filtration mechanism is loose physical trapping between grains.
Cartridge filters work by mechanical interception in fabric. The polyester pleated element traps particles in two ways - particles larger than the pore openings (10-15 microns) are physically blocked on the fabric surface, and smaller particles get trapped in the depth of the fiber structure by adhesion. The pleated element is not a loose bed like sand - it is a rigid, bonded fabric structure.
Reversed flow does not clean cartridge fabric. Reversing water flow through a cartridge element does not dislodge particles trapped in and on the fabric. The adhesion forces holding fine particles in the fiber are not overcome by a water current running the wrong direction. What reversal does do is stress the pleats in the wrong direction, potentially collapsing the pleat structure or damaging the bond between the polyester fabric and the support mesh.
There is no backwash port to connect. Cartridge filter tanks - whether a Hayward SwimClear C4020, a Pentair Clean and Clear Plus, or an off-brand unit - have one inlet and one outlet. There is no third port for waste discharge. Even if you wanted to improvise a backwash procedure, there is nowhere for the displaced water to go.
What You Do Instead - The Correct Cartridge Cleaning Procedure
The cartridge cleaning procedure is a hands-on process. Plan for 30-60 minutes the first time you do it, and 20-40 minutes once you are familiar with your filter.
Step 1: Turn off the pump. Never open a pressurized filter. The pressure inside the tank when the pump is running can be 15-30 PSI - enough to blow the lid off with force when unlatched. Turn the pump off at the timer or breaker, not just the local switch, to prevent accidental restarts.
Step 2: Release pressure using the air relief valve. Every cartridge filter has a small air relief valve on the top of the tank - it looks like a small pet cock or bleed screw. Open it slowly. You will hear air escaping and see the pressure gauge drop to zero. Wait until the gauge reads zero and no more air or water is escaping before proceeding.
Step 3: Remove the filter lid and extract the cartridge(s). Cartridge filters use either a large clamp band around the tank mid-section or a series of bolts on the top plate. Loosen the clamp or remove the bolts, then lift the lid straight up. The cartridge element (or elements - multi-cartridge filters like the Hayward C4020 have 4 elements) lift out vertically. Note the orientation so you reinstall them correctly.
Step 4: Rinse the cartridge with a garden hose. Use a straight hose nozzle - not a high-pressure jet. Hold the nozzle perpendicular to the pleats and work from the top of the cartridge to the bottom, rinsing each pleat channel. Rotate the cartridge as you go. The goal is to flush debris out of the channels, not blast it deeper into the fabric. A pressure washer will destroy the cartridge fabric - do not use one.
Step 5: Deep clean with chemical soak (monthly or as needed). Rinsing removes surface debris but does not dissolve oils, sunscreen residue, and calcium deposits that build up in the fiber over time. For a thorough clean, mix enzyme-based cartridge cleaner according to label directions (or use 1 cup of trisodium phosphate per 5 gallons of water as a budget option) and soak the cartridge overnight - at least 8 hours. After soaking, rinse thoroughly until no suds remain.
Step 6: Inspect, reassemble, and restart. Before reinstalling, hold each cartridge up to bright light and look through the pleats. Holes or tears will be visible as bright spots through the fabric. Check that the end caps are firmly bonded to the media - no lifting or cracking. If the cartridge passes inspection, reinstall in the correct orientation, seat the lid, tighten the clamp or bolts evenly, restart the pump, and allow pressure to build. Open the air relief valve briefly to purge trapped air, then close it once water streams out steadily. Note your new clean baseline PSI.
How Often to Clean a Cartridge Filter
The pressure rule is the definitive trigger: clean your cartridge filter when the pressure gauge reads 8-10 PSI above your clean baseline. Your clean baseline is the PSI reading you recorded immediately after installation or the last cleaning - write it on the filter tank with a permanent marker.
What this looks like in practice:
- You install a new cartridge and note the pressure at 10 PSI - that is your baseline.
- When the gauge climbs to 18-20 PSI, it is time to clean.
- After cleaning, the gauge should return to approximately 10 PSI (within 1-2 PSI of baseline).
Typical cleaning frequency in peak season:
- Light use, covered pool: every 4-6 weeks
- Regular family use: every 2-4 weeks
- Heavy use, uncovered pool near trees: every 1-2 weeks
- During algae blooms: potentially every 24-48 hours until the bloom is resolved
Annual deep clean: Chemical soak at least once per season, even if you are rinsing regularly. Oils and scale accumulate over time and cannot be rinsed away - only chemical soaking removes them.
Signs the Cartridge Needs Replacing, Not Just Cleaning
Cleaning restores a healthy cartridge close to its original performance. When a cartridge is at the end of its life, cleaning no longer helps. Recognize these signs:
- Pressure climbs back up within days of cleaning - the media is too clogged at the fiber level to ever rinse clean again
- Pleats are collapsed or permanently matted - the pleat structure has failed and flow area is reduced
- Visible tears or pinholes in the fabric - debris bypasses the media and returns to the pool (hold the cartridge up to bright light to check)
- End caps cracked, splitting, or separating from the media - the structural integrity of the element is compromised
- Permanent grey or brown discolouration throughout - mineral scale and oil saturation that chemical soaking cannot reverse
- Cleaning takes the pressure back only partway - if your baseline was 10 PSI and cleaning only gets you back to 14 PSI, the media is nearing exhaustion
Cartridge elements typically last 2-3 years with correct maintenance: routine rinsing, monthly deep soaks, and no high-pressure washing. Replacing cartridges on schedule, rather than running them to failure, keeps filtration quality high and avoids cloudy pool water.
Replacement cartridge cost: approximately $0.75 per sq ft. A 100 sq ft cartridge costs around $75, a 300 sq ft set (like those for the Hayward SwimClear C3020) costs approximately $225.
Cartridge Filter vs. Sand Filter Maintenance Compared
This side-by-side covers the full picture for owners deciding between the two types, or switching from one to the other.
| Feature | Sand Filter | Cartridge Filter |
|---|---|---|
| How to clean | Backwash at multiport valve (2-3 min) | Remove, spray, optional soak (30-60 min) |
| Water used per cleaning | 200-500 gallons | ~10 gallons for rinsing |
| Trigger for cleaning | Pressure +8-10 PSI above baseline | Pressure +8-10 PSI above baseline |
| Filtration fineness | 20-40 microns | 10-15 microns |
| Annual full service | Sand inspection, multiport O-ring check | Full chemical soak + cartridge inspection |
| Media replacement interval | Sand every 5-7 years ($30-60) | Cartridge every 2-3 years ($50-200+) |
| Algae bloom handling | Handles well - fast repeated backwashing | Clogs rapidly during blooms |
| Suitable without backwash drain | No | Yes |
| Best for | Large pools, low-effort owners | Most residential pools |
Sand filter advantages are entirely in the convenience of the cleaning process. Cartridge filter advantages are in filtration quality, water conservation, and suitability for properties without a backwash drain. Neither type is universally better - the right choice depends on your situation.
Related Guides
Frequently Asked Questions
Can you backwash a Hayward cartridge filter?
What happens if you try to backwash a cartridge filter?
How do you clean a cartridge filter instead of backwashing?
Is a cartridge filter harder to maintain than a sand filter?
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