How to Backwash a DE Filter - Step-by-Step Guide

The Critical Difference Between DE and Sand Filter Backwashing

The backwash procedure for a DE filter is almost identical to a sand filter - with one essential difference: after every backwash, you must add fresh DE powder.

This step is not optional. It is not a bonus maintenance task. It is the functional requirement that makes a DE filter work.

Here is why: the filtering medium in a DE filter is not the fabric grids themselves. The grids are just a support structure. The actual filtering happens in the thin layer of diatomaceous earth powder that coats those grids. Backwashing removes most of that coating. Without a fresh DE charge, water passes through bare grids and back into your pool nearly unfiltered - defeating the entire purpose of running a DE filter.

How Much DE to Add After Backwashing

Add 80% of your filter’s rated DE capacity after each backwash. The 80% rule accounts for the fact that backwashing is not 100% efficient - some old DE remains on the grids and in the underdrain area. Adding 100% of the rated DE capacity would overfill the filter.

These are starting points. Check your filter’s owner manual - the rated DE capacity is printed on the label on the filter housing.

Buy DE powder: Diatomaceous earth pool filter powder on Amazon - the standard 25 lb bag handles multiple recharges for a typical residential filter.

The Slurry Method: Why It Matters

Do not pour dry DE powder directly into the skimmer. Dry DE powder tends to clump when it hits water, and clumps do not coat grids evenly. Uneven coating means some sections of the grid filter fine particles while others do not.

The slurry method:

1. Measure your DE quantity into a clean bucket
2. Add warm water (about 1 gallon per pound of DE) and stir vigorously
3. Continue stirring until the mixture is completely smooth with no lumps
4. Pour the slurry into the running skimmer slowly over 30–60 seconds

This gives the pump time to distribute the DE evenly across all the grids rather than packing it onto the first grids nearest the inlet.

Backwash Frequency: Let the Gauge Decide

The correct trigger for backwashing a DE filter is a pressure rise of 8–10 PSI above your clean baseline - not a calendar schedule.

After every backwash and re-charge, note the pressure reading. Write it on waterproof tape on the filter housing. When the gauge reads 8–10 PSI above that number, backwash.

For most residential pools, this happens every 4–8 weeks during swim season. After a major storm, after a pool party, or at the end of a heavy swim week, pressure can rise faster. In a quiet week, you might go a full month without needing to backwash.

When Backwashing Stops Working

If your pressure rises back to the backwash trigger level within a few days of backwashing, backwashing alone is no longer sufficient. The grids have accumulated oil and grease that reversed water flow cannot remove.

This is the time for a full strip-and-clean:

1. Turn the pump off and release pressure through the air relief valve
2. Open the clamp band and remove the top of the filter
3. Pull the manifold and grids out of the tank
4. Soak grids in a dedicated DE filter cleaner (diluted per instructions) for 8–12 hours
5. Rinse each grid with a gentle garden hose spray - do not use high pressure, which damages the fabric
6. Inspect each grid for tears (hold up to light - pinholes are visible)
7. Reassemble with fresh DE

Do this full service once per season at minimum, or whenever backwashing no longer restores normal pressure.

Related Guides

• How to Backwash a Pool Filter - general procedure for sand and DE
• How Often to Backwash Pool Filter - the PSI method explained
• How Much DE for Pool Filter? - complete sizing table and first-charge quantities
• DE Filters Complete Guide - everything about diatomaceous earth filters