If your pool water is cloudy, return flow feels weak, or filter pressure is rising, it may be time to backwash the filter.
To backwash a pool filter, turn off the pump, set the multiport valve to Backwash, restart the pump and run it until the sight glass clears, then turn the pump off, switch to Rinse for 30 to 60 seconds, and return the valve to Filter. Most pool owners should only backwash when filter pressure is about 8 to 10 PSI above clean pressure. This applies to sand filters and DE filters, not cartridge filters, which must be removed and rinsed by hand.
This guide covers what backwashing does, which filters can be backwashed, when to do it, how to do it step by step, common mistakes, troubleshooting, water and cost concerns, and what to do if you have a cartridge filter.
What Does It Mean to Backwash a Pool Filter?
Backwashing sends water backward through the filter instead of in its normal direction. That reverse flow loosens and flushes out dirt, oils, and debris trapped inside the filter and sends the waste water out through the waste line.
What backwashing does for your pool system
Backwashing clears debris from the filter, restores circulation by reducing internal resistance, lowers filter pressure when the system is overloaded, and improves filtration when done at the right time. It is especially useful after storms, heavy pool use, or algae cleanup.
Which Pool Filters Can Be Backwashed?
Not every pool filter can be backwashed.
Sand filters use a multiport valve that directs water in reverse and are the most common type of backwashed pool filter.
DE (diatomaceous earth) filters can also be backwashed, but they must be recharged with fresh DE afterward.
Cartridge filters cannot be backwashed. The cartridge must be removed and rinsed manually.
When Should You Backwash a Pool Filter?
The pressure gauge is the most reliable trigger. Backwash when the reading is about 8 to 10 PSI above your clean filter pressure. If you have not recorded that baseline, note the PSI after the next full cleaning. If the gauge is stuck, cracked, or hard to read, replace it first.
Common signs your pool filter needs backwashing
Pressure is the main signal, but not the only one. Other signs include:
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Weak return jet pressure or slower water flow
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Cloudy or dull pool water, even with balanced chemistry
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Dirty or darker water in the sight glass
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A strained-sounding pump or a less efficient system
One sign alone does not always mean you need to backwash, but several signs combined with higher pressure usually do.
How often should you backwash a pool?
Backwash frequency depends on debris load, swimmer use, storms, algae blooms, and the size of the pool and filter. A lightly used backyard pool may go six weeks without needing a backwash. The same pool may need one in three days after a busy weekend and a windstorm.
Use the pressure gauge, not the calendar. Backwash when the PSI is 8 to 10 above baseline.
What You Need Before You Backwash a Pool Filter
Basic equipment and setup
Most sand and DE filter systems already have what you need: a backwash hose long enough to reach a safe drain area, a hose clamp, and a working pressure gauge. Replace any gauge that is cracked, fogged, or stuck. You should also know where your backwash water can legally discharge. In many areas, storm drain discharge is not allowed.
Safety checks before you start
Turn the pump off before moving the multiport valve. Moving the valve while the pump is running can damage the internals and crack the spider gasket. Unroll the backwash hose fully before restarting the system. A kinked hose can back up pressure. If the valve handle feels stuck, do not force it. Confirm the pump is fully off, wait a moment, and try again. Keep children and pets away from the discharge area while the system is running.
How to Backwash a Pool Sand Filter Step by Step
Step 1: Turn off the pool pump
Before touching the multiport valve, make sure the pump is completely off. Moving the valve under pressure can damage the internal gasket.
Step 2: Set the valve to Backwash
Find the multiport valve on top of or beside the filter tank. Common positions include Filter, Backwash, Rinse, Waste, Recirculate, and Closed. Move the handle firmly to Backwash and make sure it locks fully into place.
Step 3: Restart the pump and run the backwash cycle
Turn the pump back on and watch the sight glass if your system has one. Let it run until the water turns clear. This usually takes two to three minutes. If the water is still cloudy after three minutes, keep running until it clears.
Step 4: Turn off the pump and switch to Rinse
Once the discharge water is clear, turn the pump off again and move the valve to Rinse.
Step 5: Run a short rinse cycle
Turn the pump back on and run Rinse for 30 to 60 seconds. This resets the sand bed so it settles properly before water returns to the pool. If you skip it, fine sand can blow back into the pool.
Step 6: Reset the valve to Filter and restart the system
Turn the pump off again, move the valve back to Filter, and restart the pump.
Step 7: Recheck pressure and flow
Check the pressure gauge. It should read close to your clean baseline. Then check the return jets to confirm normal flow. Backwashing sends a noticeable amount of water to waste, so the pool level may drop a few inches. Add water if needed.
How to Backwash a DE Pool Filter
DE filter backwash steps
The process is similar to a sand filter. Turn off the pump, set the valve to Backwash, restart the pump, and run the cycle until the discharge water clears. Turn the pump off, switch to Rinse if your valve has that setting, run it for 30 to 60 seconds, then reset the valve to Filter.
A DE filter may need a second short backwash pass to clear the grids fully. If pressure does not drop back to baseline after the first cycle, repeat the backwash briefly, then rinse and reset again.
Add fresh DE powder after backwashing
This is the key difference from a sand filter. Backwashing flushes a significant amount of DE off the grids. If you do not replace it, the filter has little ability to capture fine debris.
Once the system is back in Filter mode and running, add fresh DE powder through the skimmer. The amount depends on your filter’s square footage, so check the filter label or the manufacturer’s instructions. Mix the measured DE with a little water in a bucket to make a slurry, then slowly pour it into the skimmer while the pump is running. The grids should be recoated within a few minutes.
Dry DE powder can irritate the lungs. Wear a dust mask when measuring and handling it.
How DE backwashing differs from sand filter backwashing
The procedure is similar, but DE filters require a recharge step every time. Skip it, and the system may circulate water without filtering it effectively.
Can You Backwash a Cartridge Pool Filter?
No. Cartridge filters do not use a multiport valve and do not have a backwash setting. The cartridge must be removed and cleaned manually.
How to clean a cartridge filter instead
Shut down the pump and relieve system pressure by opening the air relief valve on top of the filter tank. Remove the housing lid and lift out the cartridge. Rinse it thoroughly with a garden hose, spraying from top to bottom and between the pleats. For a deeper clean, soak the cartridge in filter cleaning solution for several hours or overnight, then rinse it again before reinstalling it.
After reassembly, restart the system and check the pressure. A clean cartridge should bring the gauge back close to baseline. If rinsing no longer lowers pressure, or if the pleats are cracked or damaged, replace the cartridge.
If you came here looking for backwash instructions and you have a cartridge filter, skip the valve entirely and clean the cartridge instead.
Related Reading: How to clean pool filter
Troubleshooting Pool Filter Problems After Backwashing
Why is the pressure still high after backwashing?
The most common cause is a faulty pressure gauge, so start there. If the gauge is working, the problem may be a partially blocked return line, a valve that did not reset fully to Filter, or internal filter damage such as cracked laterals in a sand filter or collapsed grids in a DE filter. If repeated backwashing does not lower the pressure, inspect the filter tank.
Why is the backwash water not draining properly?
Check the hose first. A kink or tight bend can restrict flow significantly. Then confirm the valve is fully set to Backwash. In some cases, the waste line is blocked or the hose route runs uphill too far for the pump to push effectively.
Why is the pool still cloudy after backwashing?
Backwashing cleans the filter. It does not clear the pool instantly. If the water is still cloudy right afterward, give the system time to circulate and recapture suspended particles. If the pool stays cloudy for more than a day after a successful backwash, the issue is more likely pool chemistry. Check pH, alkalinity, and sanitizer levels.
How can you tell if the filter plumbing or valve setup is wrong?
This comes up most often with DE filters and newly installed systems. If flow seems reversed, pressure spikes immediately after backwashing, or the backwash water looks clean from the start, there may be a plumbing or setup issue. If the system was recently installed or serviced, have a pool professional verify the plumbing orientation.
Common Pool Backwashing Mistakes That Cause Bigger Problems
Moving the multiport valve while the pump is running
This is the most damaging and most preventable mistake. The spider gasket is not designed to handle flow switching under pressure. One turn at the wrong time can crack it and cause the valve to leak between settings.
Skipping the rinse cycle on a sand filter
After backwashing, the sand bed is unsettled. Without rinsing, fine sand can blow back through the return lines and into the pool.
Backwashing too often or not often enough
Backwashing too often wastes water and can wash out the fine particle layer that helps a sand filter catch smaller debris. Backwashing too rarely allows the filter to clog badly enough to strain the pump and reduce water quality. Use the pressure gauge to decide.
Misreading the pressure gauge
A broken gauge is useless. If it never returns to zero, has a cracked face, or reads the same pressure regardless of filter condition, replace it. And always compare the reading to your clean baseline.
Using the wrong valve position or a poorly placed backwash hose
A valve that is not fully engaged may not flow correctly and can send water back to the pool during the cycle. A hose that is not fully unrolled or securely clamped can whip around when the pump starts.
How Much Water Does Backwashing Use?
A pool backwash usually uses about 200 to 300 gallons of water per cycle. The exact amount depends on the filter size and run time, and repeated backwashing also means more refilling and chemical rebalancing.
How to reduce unnecessary backwashing
The easiest way to backwash less often is to keep larger debris out of the filter. Empty skimmer baskets and pump baskets regularly.
A robotic pool cleaner can also reduce the debris load on the filter by capturing dirt and leaves in its own basket instead of sending them through the main filtration system. Less debris reaching the filter usually means less frequent backwashing and less wasted water.
Do not backwash on a fixed schedule if the pressure has not reached the 8 to 10 PSI trigger.
Where Does Pool Backwash Water Go?
Backwash water contains algae, debris, oils, and pool chemicals, so it cannot be discharged just anywhere. In many areas, discharge to a sanitary sewer cleanout or a vegetated area may be allowed, while discharge to storm drains, curbs, or drainage ditches is restricted or prohibited. Check local rules before choosing a discharge point. When in doubt, ask your local water district or municipality.
What Does Pool Backwashing Cost?
Pool backwashing usually costs a few dollars per cycle. In most cases, a backwash uses about 200 to 300 gallons of water, which works out to roughly $2 to $5 in water cost, plus extra chemicals to rebalance the pool afterward. If you have a DE filter, you also need to add the cost of fresh DE powder after each backwash. To keep costs down, backwash only when filter pressure rises instead of doing it on a fixed schedule.
Quick Backwash Checklist for Pool Owners
Before you backwash
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Confirm your filter type: sand, DE, or cartridge
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Check that pressure is 8 to 10 PSI above baseline
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Turn the pump completely off
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Unroll and position the backwash hose
During the backwash
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Make sure the valve is fully set to Backwash
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Watch the sight glass or discharge water and run until clear
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Stay with the system while it is running
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Turn the pump off before changing valve positions again
After the backwash
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Run Rinse for 30 to 60 seconds on sand and DE filters
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Reset the valve fully to Filter
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Restart the pump and confirm pressure drops near baseline
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Check the water level and add water if needed
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For DE filters, add fresh DE powder through the skimmer
Frequently Asked Questions About How to Backwash a Pool
Can you backwash a pool pump?
No. The filter gets backwashed, not the pump. The pump powers the process, but the filter is the part being cleaned.
Do you backwash with the pump on or off?
Turn the pump off before moving the multiport valve. Turn it back on only after the valve is set correctly. The pump runs during the backwash cycle, but it must be off during every valve change.
How many minutes should you backwash a pool filter?
Usually two to three minutes, but the better guide is the sight glass or discharge water. Run the cycle until the water turns clear. A very dirty filter may take four to five minutes.
When should you not backwash a pool?
Do not backwash unless the pressure gauge indicates it. Backwashing too early wastes water. You should also avoid backwashing right after adding flocculant, since flocculant is meant to help particles settle so they can be vacuumed out.
Do you backwash or rinse first?
Always backwash first, then rinse. Backwashing flushes out the debris. Rinsing settles the filter media before normal filtration resumes.
Do you have to rinse after backwashing?
For sand and DE filters, yes. Skipping the rinse cycle can send fine sand or debris back into the pool. Cartridge filters are not backwashed, so this does not apply to them.
Can you backwash a cartridge pool filter?
No. Cartridge filters must be opened, removed, and cleaned by hand.
Why is the pressure still high after backwashing?
Possible causes include a faulty gauge, a partially blocked return line, a valve that did not reset fully, or internal filter damage. If another short backwash does not fix it, inspect the filter more closely.
Final Thoughts
Backwashing a pool filter is simple once you know your filter type, valve settings, and clean pressure baseline. The key is to do it at the right time and in the right order. Too soon wastes water. Too late puts extra strain on the system.
To backwash less often, reduce how much debris reaches the filter. A cordless robotic pool cleaner can remove dirt, leaves, and settled debris before they add to the filter load, helping keep pool maintenance easier and more consistent.