Backwashing is how sand and DE filters clean themselves. Water flow is reversed through the filter, lifting the debris off the media and out through the waste line. A filter that backwashes on schedule keeps pressure low, flow steady, and the pool clear. A filter that does not backwash on schedule loses flow, strains the pump, and lets debris build up in the pool.
Backwashing is how sand and DE filters clean themselves. Water flow is reversed through the filter, lifting the debris off the media and out through the waste line. A filter that backwashes on schedule keeps pressure low, flow steady, and the pool clear. A filter that does not backwash on schedule loses flow, strains the pump, and lets debris build up in the pool.
This guide covers backwashing sand filters and DE filters, recharging DE filters with new media, when to backwash (and when not to), and what to do if you have a cartridge filter (no backwash; you clean the cartridges instead).
If your filter is older, the multiport valve sticks, or you suspect the media itself is at end of life, WETYR Pools provides filter service and media replacement across our maintenance markets. Use the form on this page or email [email protected].
Sand filter: backwashes. Filter media is sand, lasts 5 to 7 years before replacement. Easiest to operate. Filters down to about 20 microns. Examples: Hayward Pro Series, Pentair Tagelus.
DE (diatomaceous earth) filter: backwashes, then needs to be recharged with new DE media added at the skimmer. Filters down to 3 to 5 microns (the finest residential filtration). Needs media replenishment after every backwash. Examples: Hayward ProGrid DE, Pentair FNS Plus.
Cartridge filter: does not backwash. Filter media is a pleated cartridge that is removed from the housing, rinsed clean with a hose, and replaced. Filters down to 10 to 20 microns. Cartridges last 2 to 5 years. Examples: Pentair Clean and Clear Plus, Hayward SwimClear.
Backwash when filter pressure (read on the gauge at the top of the filter) rises 8 to 10 psi above the clean-baseline pressure. Clean baseline is the pressure reading after a fresh backwash or media change; typically 8 to 14 psi. When the gauge reads 16 to 24 psi, time to backwash.
Frequency: typical residential pool backwashes every 2 to 4 weeks during the swim season. After heavy debris (storms, pollen, dead algae from a shock), backwash sooner. Backwashing too often wastes water and strips DE before it does its job; backwashing too rarely strains the pump.
Do not backwash on a schedule (weekly, monthly). Backwash on pressure. The gauge is the indicator, not the calendar.
Always shut off the pump before turning the multiport valve. Turning a multiport under pressure damages the valve seals and shortens the valve life. Off, turn, on. Every time.
On most multiport valves, lift the handle slightly (it has a spring-loaded lock) and rotate to the BACKWASH position. The valve will click into place. Do not force the handle past resistance; lift first.
Backwash water exits through the waste line. If you have a fixed waste line plumbed to a drain or yard area, no action needed. If you backwash to a flat backwash hose, roll it out so water can exit. Backwash water is pool water with debris; do not run it to a sensitive plant or storm drain in some municipalities.
Start the pump. Watch the sight glass on the multiport valve (a small glass window where you can see exiting water). Water will be cloudy and dirty at first. Continue until the sight glass runs clear; typically 2 to 3 minutes for a sand filter, 3 to 5 minutes for a DE filter.
After backwash, turn pump off. Rotate the multiport handle to RINSE. Turn pump on for 30 seconds. Rinse settles the sand or DE media after backwash agitation; without rinse, debris would blow back into the pool on the next normal cycle. Turn pump off.
Pump off. Rotate the handle to FILTER. Turn pump on. The filter is now back in normal operation. Read the new pressure on the gauge; it should be back near the clean baseline (8 to 14 psi typically). This is your new reference.
DE filters only: after every backwash, you must add new DE media at the skimmer. Dose: per the manufacturer (typically 1 pound of DE per 5 square feet of filter area). Mix DE with pool water in a bucket to make a slurry, then pour into the skimmer with the pump running. The DE coats the grids and the filter resumes normal operation. Skipping this step ruins filtration and damages the grids.
Backwashing loses 200 to 500 gallons of pool water depending on filter size and backwash duration. Top off to operating level (mid-skimmer) after backwashing. Test chemistry after topping off and adjust if needed; new fill water can shift alkalinity, calcium, and pH.
Backwashing is straightforward DIY. Sand filters are the simplest; DE filters add one step (DE recharge). Most homeowners learn to backwash on the first try and do it routinely.
Call a pro when: the multiport valve sticks or leaks, pressure does not drop after backwashing (suggests channel formation in the sand bed, requires media replacement), DE blowback into the pool (broken grid, requires repair), or sand in the pool after backwashing (broken lateral inside the filter, requires teardown).
WETYR Pools provides filter service across our maintenance markets, including backwashing, media replacement (sand every 5 to 7 years, DE grids every 7 to 10 years, cartridges every 2 to 5 years), multiport valve service and replacement, and lateral repair on sand filters.
Cost for a media change: sand $200 to $400 (sand and labor), DE grid set replacement $400 to $800, cartridge replacement $150 to $400. Multiport valve replacement: $150 to $350 parts plus labor. Filter teardown for lateral repair: $200 to $500 labor plus parts. Filter included in weekly service: $125 to $225 per month covers pressure monitoring and routine backwashing.
Empty skimmer and pump baskets weekly. Use a robotic cleaner to remove fine debris before it reaches the filter. Vacuum to waste for dead algae after shocking. Run the pump enough hours for full water turnover daily (8 to 12 hours typical). Use a flocculant before vacuuming for very fine debris instead of relying on the filter alone.
A correctly sized filter (often slightly oversized) backwashes less often. If you backwash weekly and still cannot maintain pressure, the filter may be undersized for the pool or the media is at end of life.
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20 of the most-asked questions on Reddit, Quora, and pool owner forums, answered by the WETYR Pools team.
When filter pressure rises 8 to 10 psi above the clean baseline. Typical residential pool: every 2 to 4 weeks during the swim season. After heavy debris events (storms, pollen, post-shock algae), sooner. Do not backwash on a calendar; backwash on pressure.
Read the gauge right after a fresh backwash and rinse. That is your clean baseline (typically 8 to 14 psi for residential filters). Write it down on a label stuck to the filter. When the gauge reads 8 to 10 psi above that, time to backwash.
It routes water to different paths: FILTER (normal operation), BACKWASH (reverse flow to clean media), RINSE (resettle media after backwash), WASTE (bypass filter for vacuuming to waste), CLOSED (block flow for service), RECIRCULATE (skip filter for emergency circulation). Only turn the handle with the pump off.
No. Cartridge filters have no multiport valve and no backwash function. Cleaning a cartridge filter means removing the cartridges from the housing, hosing them down, and reinstalling. Replace cartridges every 2 to 5 years.
Watch the sight glass. 2 to 3 minutes is typical, but the visual is the rule: stop when the water exiting through the sight glass runs clear. Then turn off the pump and rotate to RINSE for 30 seconds.
3 to 5 minutes typical, again watching the sight glass. DE filters need slightly longer because the DE coating is the actual filter; you are flushing it off the grids before recharging.
Common causes: sand has channeled (water flows around hard-packed sand without cleaning effectively, requires sand replacement), DE grids are clogged with debris and need to be removed and cleaned individually, multiport valve is stuck partway between settings, or the pressure gauge itself has failed.
Yes. DE filters require DE media recharge after every backwash. Dose: 1 pound per 5 square feet of filter grid area, premixed in water as a slurry, poured into the skimmer with pump running. Without DE recharge, the filter does not filter.
Per the filter manufacturer. Common: 48 sq ft filter needs about 5 to 6 pounds. 60 sq ft filter needs about 6 to 7 pounds. 72 sq ft filter needs about 7 to 9 pounds. Read the side of the filter housing or the manual; over-DE-ing and under-DE-ing both reduce filtration.
A broken lateral inside the filter (the laterals are the spoke-like assemblies at the bottom that distribute flow). Repair: teardown the filter, replace the lateral. Cost: $200 to $500 in labor plus parts. Or sand has aged and become fines that pass through laterals; requires sand replacement.
Both, in some cases. Backwash before to start with a clean filter; backwash after if the vacuum loaded the filter heavily. For light vacuuming, before is enough. For post-storm or post-shock vacuuming, both.
5 to 7 years typically. Sand grains break down over time into fines that no longer filter effectively. Signs of end of life: pressure drops slowly after backwash, water clarity not as good as before, frequent backwashing needed.
7 to 10 years typically. Signs of end of life: DE blowing back into the pool through tears, grids visibly torn or warped, pressure drops irregular. Replacement: $400 to $800 for a full set.
2 to 5 years depending on use and chemistry. Quality cartridges (Pleatco brand) at the high end. Signs of end of life: cleaning does not reduce pressure, pleats are crushed or torn, deep staining.
Yes. WETYR Pools provides filter service across our maintenance markets, including media replacement, multiport valve service, grid replacement, cartridge replacement, and lateral repair. Request through the form on this page or email [email protected].
Local rules vary. Some municipalities require backwashing to a permeable yard area or to the sanitary sewer (not the storm drain) due to chlorine and DE content. Check your local ordinance. Pool backwash water with DE is also regulated as a non-hazardous waste in some areas.
Backwash reverses flow through the filter media to lift debris out the waste line. Rinse runs forward flow briefly to resettle the media and flush any residual debris out the waste line before returning to normal FILTER position. Always rinse after backwash.
Spider gasket inside the multiport is worn or damaged. Replace the gasket ($20 to $40 part) or the entire multiport ($150 to $350). Common after 5 to 10 years of use; multiport handles wear from normal operation.
Possible: DE was not recharged (DE filter), debris immediately recolonizes from a dirty pump basket or skimmer, or pressure gauge itself is stuck or failing. Empty baskets, verify DE recharge, and tap the pressure gauge to verify it moves freely.
No; backwashing inherently exhausts water out the waste line. Plan to top off after every backwash. Typical loss: 200 to 500 gallons. If you cannot afford the water loss, switch to a cartridge filter (cleaning cartridges with a hose uses less water).
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