What is a DE filter for a pool?

DE Filter
DE Filter

What is a DE Filter?

A diatomaceous earth filter known for short as a "DE" filter, is composed of several grids that capture the diatomaceous earth powder coating the grids which make up the filter media.DE filters are sometimes known in the business as "water polishers" since they are capable of filtering particles as small as 3 microns. To give you an idea of how small this is, a grain of salt is about 90 microns in size. Anything smaller than 35 microns is invisible to the naked eye. This is why in my other articles I tend to rave so much about DE filters. It is 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 less problems than with other filters. In my article on cleaning a green pool, you will notice that I did not need to vacuum the pool to waste since the DE filter captured every bit of what was being captured. 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
make sure you have a functioning pressure gauge
make sure you have a functioning pressure gauge

DE filter maintenance

Are these filters easy to maintain? Absolutely. On an average they will be back-washed once a month. Grid inspection is recommended after a year to check for rips or tears on the grid material and rinsed out thoroughly as the DE can build up over long periods of time. If a grid is torn, they can simply be replaced. They can be re-covered but buying new grids cost about the same and is much easier. Here is an example of a torn grid.


shut off the pump and position valve to "backwash"
shut off the pump and position valve to "backwash"
filter being backwashed
filter being backwashed

Back-washing 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 lets say normal clean filter pressure runs around 22 PSI. If gauge is reading 25 or 26 psi, it just means the filter is doing it's job and starting to get dirty. Rule of thumb is usually when pressure reaches 10 psi higher than normal clean filter pressure, it's time to back-wash. In this scenario it would need to be 30 to 32 psi to indicate that it needs to be back-washed.




return to filter position
return to filter position
add DE powder through skimmer
add DE powder through skimmer

Backwashing continued...

Before you position the "multi-port" valve, be sure the pump is OFF. Select the backwash position then turn the pump on. Backwash for 3 minutes. This will get a lot of the old DE powder out. I usually return to the filter position and run for a minute, and then backwash again for another minute. This ensures the filter grids are clean.

With the valve positioned back to the "filter" position, and pump running, you will add around 4 pounds of DE powder through the skimmer. (consult your DE filter's owners manual on your filters 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.

How to tell if grids are bad

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

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