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What Is a DE Pool Filter and How Does It Work?

Updated on June 5, 2017
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Being in the pool service industry for so many years, I have taken apart and serviced literally hundreds of DE filters

DE Filter
DE Filter

What is a DE Filter?

A diatomaceous earth filter (aka a DE filter) is composed of several grids that hold the diatomaceous earth powder. They are sometimes known in the business as "water polishers," since they are capable of filtering particles as small as three microns (in comparison, a grain of salt is about 90 microns in size). Anything smaller than 35 microns is invisible to the naked eye. This is why I tend to rave so much about DE filters. They are by far the best filtration available for swimming pools.

A DE filter requires back-washing less often than sand or cartridge filters. With a good working DE filter, your pool water will have far fewer problems than with other filters. In my article about how to clean a green pool, I was able to vacuum the pool without by-passing the filter to an external drain source since the DE filter captured every bit. A cartridge or sand filter would have allowed the algae to shoot back to the pool through the returns.

Torn Filter Grid
Torn Filter Grid

DE Filter Maintenance

Are they easy to maintain? Absolutely.

  • On average, it will only need to be back-washed once a month.
  • Grid inspection is recommended after a year. Check for rips or tears on the grid material and rinse thoroughly, as the DE can build up over long periods of time.
  • If a grid is torn, it can simply be replaced. It can be re-covered, but buying a new one costs about the same and is much easier.

Make sure you have a functioning pressure gauge.
Make sure you have a functioning pressure gauge.

How to Back-Wash the DE Filter

This is a pretty simple procedure. After you have done this a few times, you'll get to know what the normal clean filter pressure is for your system. This depends on pump horsepower, returns, etc. They all vary.

In this case, let's say normal clean filter pressure runs around 22 PSI. If the gauge is reading 25 or 26 PSI, that just means the filter is doing its job and starting to get dirty. In this scenario, it would need to be 30 to 32 PSI to indicate that it needs to be back-washed.

Shut off the pump and position valve to "backwash."
Shut off the pump and position valve to "backwash."
Filter being backwashed.
Filter being backwashed.
  1. Before you reposition the "multi-port" valve, be sure the pump is off.
  2. Select the "backwash" position then turn the pump on.
  3. Backwash for three minutes. This will get a lot of the old DE powder out.
  4. I usually return the valve to the "filter" position and run for another minute, and then backwash again for another minute. This ensures the filter grids are clean.
  5. With the valve positioned back to the "filter" position and the pump running, you will add around four pounds of DE powder through the skimmer. (Consult your DE filter's owners manual to discover your filter's square footage and exactly how much powder to add.)

That's it! you're done. Keep an eye on the pressure gauge and you shouldn't need to back-wash for about a month.

Return to "filter" position.
Return to "filter" position.

How to Tell If Grids Need Replacing

There is a very easy way to tell. When you add the DE powder, wait for a minute. If you have torn grids or a broken manifold, the DE powder will come right back into the pool through the returns. Time to take the filter apart!

Add DE powder through skimmer.
Add DE powder through skimmer.

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