- Backwash your pool filter when the pressure gauge reads 8 to 10 PSI above its normal clean operating pressure, or about every 1 to 4 weeks, depending on your filter type and pool use.
- For sand and DE filters, turn off the pump, move the multiport valve to Backwash, run the pump for 2 to 3 minutes until the sight glass runs clear, then switch to Rinse for 30 seconds before returning the valve to Filter.
- Cartridge filters cannot be backwashed. Instead, remove the cartridge and rinse it thoroughly with a garden hose. Attempting to backwash a cartridge filter can damage the filter element.
- Every backwash cycle uses roughly 200 to 300 gallons of water, and DE filters require fresh DE powder afterward. For Arizona pool owners, timing your backwash correctly helps conserve water while keeping your filtration system performing at its best.
Cloudy water and weak water flow don't always mean something is broken. Sometimes, your pool filter is simply full of the dirt and debris it's been working hard to catch. Learning how to backwash pool filter systems is one of the easiest ways to restore proper filtration and improve water circulation.
At ePoolSupply, we know a filter doesn't suddenly stop working overnight. Debris builds up, pressure rises, and eventually your system lets you know it needs attention. If that's where you're at, we'll walk you through how to backwash your filter, explain what changes between filter types, and point out a few common mistakes before they become bigger problems.
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What Is Backwashing and Why Does It Matter?
Backwashing reverses the flow of water through a sand or DE filter, flushing trapped dirt and debris out through the waste line instead of allowing it to build up inside the filter. When you backwash pool filter systems at the right time, your filter can continue to trap debris and circulate clean water throughout your pool.
(This process only applies to sand and DE filters. Cartridge filters are cleaned differently, which we'll cover later in this guide.)
How a Multiport Valve Works
The multiport valve sits on top of or beside your filter tank and directs water through different parts of the filtration system. Depending on the setting, it can filter, backwash, rinse, send water to waste, recirculate, or close the system.
As explained in Hayward's multiport valve operation guide, most multiport valves include six positions: Filter, Backwash, Rinse, Waste, Recirculate, and Closed. Before moving the handle, always turn the pump off completely. Rotating the valve while the system is under pressure can damage the spider gasket inside the valve.
If worn O-rings or handles are making the valve difficult to operate, replacing them with the correct Hayward filter parts and accessories often restores smooth operation.
Sand vs. DE vs. Cartridge — Which Filters Can Be Backwashed?
One of the biggest points of confusion we hear from pool owners is whether every filter can be backwashed. The answer depends on the type of filter you have.
As you'll see when comparing a cartridge vs. DE vs. sand filter, sand and DE filters are both designed with a backwash cycle, while cartridge filters are cleaned by removing and rinsing the filter element. DE filters also require fresh DE powder after every backwash so they continue filtering effectively.
When Should You Backwash Your Pool Filter?
While pool owners sometimes rely on a schedule, your filter's pressure gauge lets you know when debris has built up enough to affect performance and when it's time to backwash. Factors like algae cleanup and increased pool use can also mean it's time to backwash sooner than usual.
Reading Your Pressure Gauge Correctly
Start by recording your filter's clean operating pressure after a fresh cleaning or at the beginning of the season. That reading becomes your baseline for future maintenance.
Once the pressure gauge rises to 8 to 10 PSI above that clean baseline, it’s backwash time. If you haven't recorded your baseline yet, do the following:
- Perform a complete backwash
- Rinse out the filter
- Use the new pressure reading as your reference moving forward
On the other hand, pressure that's consistently lower than normal may indicate that you have air in your pool lines rather than a dirty filter.
Arizona-Specific Backwash Frequency
Most pools need backwashing every 1 to 4 weeks, but Arizona pools often need more frequent attention because they run much longer throughout the year and monsoon season can load filters with dust and debris almost overnight.
During the summer, we recommend checking your pressure gauge every week instead of waiting for water clarity to change. A complete backwash cycle typically only takes 2 to 3 minutes, followed by a 30-second rinse cycle before returning the valve to Filter.
How to Backwash a Pool Filter — Step-by-Step by Filter Type
Before starting any backwash, always turn the pump off completely. Never rotate the multiport valve while the pump is running. The pressure inside the system can damage the spider gasket, turning a routine maintenance task into a much larger repair.
How to Backwash a Sand Filter
Sand filters are straightforward to backwash, but following each step in the proper order helps remove debris while protecting the filter media.
- Turn off the pump. Wait until all water movement has stopped before touching the multiport valve.
- Connect your backwash hose to the waste port if one isn't permanently plumbed. Direct the water to an approved drainage area. Arizona homeowners can often discharge backwash water into landscaping, but always check local requirements first.
- Move the multiport valve to Backwash.
- Turn the pump on and run it for 2 to 3 minutes, or until the sight glass runs clear.
- Turn the pump off, move the valve to Rinse, and run the pump for 30 seconds.
- Turn the pump off again, move the valve back to Filter, and restart the system. Your pressure gauge should return close to its clean baseline.
If the pressure doesn't drop after backwashing, old filter sand, channeling, or damaged sand filter laterals could be preventing the filter from working properly.
How to Backwash a DE Filter
The backwash process is very similar for DE filters, but there's one important difference: the filter must be recharged with fresh DE powder before it's ready to go back into service.
- Turn off the pump.
- Move the multiport valve to Backwash.
- Run the pump for about 2 to 3 minutes. A cloudy, milky discharge is normal as the old DE powder and trapped debris are flushed from the filter.
- Rinse the filter. Turn the pump off, switch the valve to Rinse, and run the pump for about 30 seconds before shutting it off again.
- Return the valve to Filter and restart the pump.
- Add fresh DE powder. Mix the correct amount of DE powder with water in a bucket, then slowly pour the slurry into the skimmer while the pump is running. Most filters require about 1 pound of DE per 10 square feet of filter area, so check your filter label to determine the correct amount.
- Allow the DE to coat the filter grids. Once the slurry has been added, the filter is ready to resume normal operation.
Skipping fresh DE after backwashing leaves the filter grids unprotected, allowing fine debris to pass through the system and potentially shortening their life. If a backwash no longer improves performance, worn pool filters or internal components may be the next place to look.
Why Cartridge Filters Cannot Be Backwashed
Cartridge filters don't have a backwash cycle. Trying to backwash a cartridge filter can damage the pleats and force debris deeper into the filter media.
Instead, turn off the pump, release the pressure inside the filter housing, remove the cartridge, and rinse between each pleat with a garden hose, working from the top down. Avoid using a pressure washer, as it can damage the filter material. If the cartridge is heavily soiled, soak it in a cartridge cleaning solution before reinstalling it.
Common Backwashing Mistakes to Avoid
A proper backwash only takes a few minutes, but skipping a step can create bigger problems than the dirty filter you started with.
You should avoid:
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Turning the Multiport Valve While the Pump Is Running: Always shut the pump off completely before moving the valve. Changing positions while the system is under pressure can damage the spider gasket.
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Stopping the Backwash Cycle Too Soon: Let the cycle run until the sight glass is clear. Ending it early leaves debris inside the filter, so pressure can build up again quickly.
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Skipping the Rinse Cycle: The rinse cycle settles the filter media before normal filtration resumes. Skipping it can send fine particles back into the pool, leaving the water cloudy.
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Forgetting to Re-Add DE Powder: Every DE filter needs fresh DE powder after backwashing. Running the system without it reduces filtration performance and can damage the filter grids over time.
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Backwashing Too Often: Your pressure gauge should determine when it's time to backwash, not the calendar. Cleaning the filter too often wastes water and can reduce filtration efficiency.
- Ignoring Water Loss: A typical backwash uses 200 to 300 gallons of water. Top off the pool afterward to maintain the proper water level and help prevent the pump from drawing in air.
Backwashing solves many filter problems, but not all. If your pressure stays high, your water still looks cloudy, or something just doesn't seem right, don't assume you need to replace the entire filter.
At ePoolSupply, we help pool owners troubleshoot these issues every day and know that the right diagnosis can mean fewer repairs and more time in the water. If you're still unsure how to backwash pool filter systems correctly, we're here to help you get your pool back on track.
FAQs: Backwashing Your Pool Filter
How do I know when to backwash my pool filter?
Don't guess or rely on the calendar. Your pressure gauge is the best indicator. Once the reading climbs 8 to 10 PSI above your filter's clean baseline, it's time to backwash. For most pools, that works out to every 1 to 4 weeks, although Arizona pools may need it more often when monsoon season comes around.
How long should I run the backwash cycle?
It doesn't take long. Run the pump on the Backwash setting for 2 to 3 minutes, or until the sight glass runs clear. Then switch to Rinse for 30 seconds before returning the valve to Filter.
Can you backwash a cartridge pool filter?
No. Cartridge filters are designed to be removed and cleaned by hand. Trying to backwash one can damage the pleats and reduce filter performance.
Why is my pool still cloudy after backwashing?
Don't assume the backwash didn't work. Cloudy water often means the rinse cycle was skipped, fresh DE powder wasn't added to a DE filter, or the filter media has reached the end of its service life. If the pressure climbs again soon after backwashing, consider taking a closer look at the filter.
How much water does backwashing use?
A typical backwash uses about 200 to 300 gallons of water, depending on your filter and how long the cycle runs. Once you're finished, top off the pool so the water level stays high enough for the pump to operate properly.