Domakihub How to Backwash a DE Pool Filter the Right Way
Keep your diatomaceous earth filter running at peak efficiency with this simple backwash routine.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
A DE (diatomaceous earth) filter delivers some of the clearest pool water available, but it earns that reputation only when the filter grids are clean. Backwashing reverses the flow of water through the filter, flushing trapped debris and spent DE powder out through the waste line so fresh powder can do its job again. The video above covers the full visual process; the steps below give you a precise, repeatable routine whether you manage a private villa in Crete, a holiday rental on Mykonos, or a small hotel pool anywhere in Greece.
Why DE Filters Need Regular Backwashing
A DE filter works by coating a set of fabric-covered grids with a thin layer of diatomaceous earth powder. Water passes through this powder cake, which traps particles as small as 3–5 microns — far finer than sand or cartridge filters can manage. Over time, the powder cake becomes loaded with dirt, algae spores, and mineral deposits, causing the filter pressure to climb and water flow through the returns to drop.
When the pressure gauge reads 8–10 PSI above your filter's clean starting pressure, it is time to backwash. In the Greek climate, with heavy sunscreen use from guests and intense summer UV driving algae growth, pools in active use often need backwashing every two to four weeks rather than monthly.
What You Need Before You Start
You need fresh DE powder (the same amount originally charged into the filter — check your filter's label, typically 1 kg per 10 m² of filter area), a bucket or measuring cup, and access to the backwash valve on the filter. Identify where your backwash hose drains: Greek regulations prohibit discharging chemically treated water directly into storm drains or soil near protected vegetation, so direct the hose to an appropriate sewer connection or holding point.
Note the current pressure reading on the gauge before you start. Write it down — this becomes your new reference 'clean' pressure after the procedure is complete.
Step-by-Step: How to Backwash a DE Pool Filter
- 1
Turn off the pump completely
Always shut the pump off at the breaker or timer before touching the multiport or slide valve. Rotating a multiport valve while the pump is running tears the internal spider gasket — a repair that costs far more than a backwash takes. Wait a full five seconds after the pump stops before moving the valve handle.
- 2
Set the valve to Backwash
On a multiport valve, press the handle down to disengage the locking pin, turn it to the BACKWASH position, and release. On a push-pull slide valve, pull the handle straight up until it locks. Attach the backwash hose to the waste port if it is not already connected, and direct the other end to an approved drain point.
- 3
Run the pump until the sight glass clears
Switch the pump back on and watch the sight glass (the small transparent window on the waste line). Water will first run milky white as dirty DE and debris flush out. Continue running for two to three minutes, or until the water in the sight glass runs visibly clear. Do not stop early — cutting the cycle short leaves contaminated powder on the grids.
- 4
Rinse the filter before returning to normal
Turn the pump off again, move the valve to RINSE, then restart the pump for about 30 seconds. This settles any remaining debris to waste rather than sending it back to the pool. Without this rinse step, a cloud of dirty water can enter the pool the moment you return to filter mode. Turn the pump off once more and return the valve to FILTER.
- 5
Recharge with fresh DE powder
Measure the correct amount of DE powder — typically 75–80% of the original charge, because backwashing does not strip the grids completely clean. Mix the powder with water in a bucket to form a slurry, then pour it slowly into the skimmer closest to the pump while the pump is running on FILTER. The current carries the powder to the grids within a few minutes. Check the pressure gauge: it should be close to your recorded clean baseline. If it is still elevated, repeat the backwash or plan a full grid teardown-and-clean.
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FAQ
- How often should I backwash a DE filter on a holiday rental pool in Greece?
- During peak summer season (June–August), plan on backwashing every two to three weeks if the pool is in daily use. Heavy bather load, sunscreen, and intense UV all accelerate the saturation of the DE cake. Track the pressure gauge rather than the calendar — backwash whenever the reading climbs 8–10 PSI above the clean baseline, regardless of how recently you last did it.
- How much DE powder do I add after backwashing?
- Add roughly 75–80% of the filter's original powder charge. A full backwash does not remove every trace of DE from the grids, so topping up to 100% risks over-pressurising the filter. Check the filter manufacturer's label for the original charge weight, then calculate accordingly — for most residential and small commercial filters in Greece this is between 0.8 kg and 2.5 kg.
- Can I discharge backwash water into the garden or the sea?
- No. Backwash water contains concentrated chlorine, cyanuric acid, and algaecide residues that damage plants and marine ecosystems. In Greece, pool operators are required to route waste water to an approved sewer connection. If your property lacks a suitable connection, consult your local municipality for compliant disposal options before operating the filter.