What Is a DE Pool Filter?

Swimming pool cleaning and repairs


DE stands for diatomaceous earth, which is sedimentary rock composed of chemically inert, fossilized (or skeletal) remains of billions of microscopic algae-like organisms, called diatoms. These skeletons are called silica, and silica deposits are mined from rivers, lakes, oceans, and streams. Silica makes up about 26 percent of the earth's crust by weight. Various forms of this natural substance include sand, emerald, quartz, feldspar, mica, clay, asbestos, and glass.

There are three types of filters used for pools: sand, cartridge, and diatomaceous earth (DE). Many pool owners and pool maintenance workers consider DE filters to be the best type of filter for a residential swimming pool. Why? Among their advantages, DE filters are compact and filter out smaller particles than the other types of filters.

Uses for Pool Filters

DE, the abovementioned white powdery substance, is similar to dinosaur bones, according to pool expert Terry Tamminen, author of The Ultimate Guide to Pool Maintenance. If you examine diatomaceous earth (DE) under a microscope, maintains Tamminen, you will see tiny sponge-like organisms, which explains DE's ability to absorb or filter water's impurities. Since the DE is so fine, it can filter extremely small—microscopic-sized—particles from the water as it passes through.

When adding DE to a filter, some pool pros recommend using 1/2-cup less than the instructions of whatever brand you use. Why? There's always leftover DE powder no matter how well you clean. Too much DE can end up clogging the skimmer, creating additional problems. Less, as they say, is more.


DE can be purchased at hardware stores, pool supply stores, and grain and feed supply stores.

Food Grade DE

Food-grade DE does not mean you'll be serving up DE burgers at your next barbecue. Don't even think about it. Fresh-water food grade diatomaceous earth is the type used in agriculture for grain storage, and as a feed supplement for livestock and farm animals.

City Requirements

Because DE could potentially clog pipes, some cities and counties do not allow it to be dumped into sewer systems. Instead, a separation tank is added next to the DE filter. When the filter is drained or backwashed, the dirty water passes through a canvas strainer bag inside a small tank before reaching the sewers or storm drains. Most of the DE is retained in the strainer bags, which can then be discarded.

Control Bed Bugs and Fleas

DE has long been used for pest control because that fine, absorbent powder causes insects' exoskeletons to dehydrate and die. DE can be found in snail and slug repellents and is used to control cockroaches and fleas. In the garden, DE can be a lethal dust to aphids, ants, thrips, mites, and earwigs. It is not harmful to beneficial worms.

And yes, the infamous bedbug can be eradicated by DE, although it can take several weeks to do the job.

Other Uses

DE is also used in cat litter, to filter drinking water, in fish tanks, and in beer and wine. Diatomaceous earth is sometimes used to filter syrup, sugar, and honey.

Because of its abrasive properties, DE has been used in toothpaste, metal polishes, and facial scrubs. Other uses for DE include:

  • As an ingredient in bonsai soil
  • As an additive in cement
  • Dewormer
  • A filler in many products such as paints and dry chemicals
  • In chemistry as a filtration aid