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Swimming Pool Terms Glossary

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D. E. filter – also called a diatomaceous earth filter – A filter designed to use diatomaceous earth (D.E.) as the filter medium. The D.E. is added through the skimmer with the pump on which takes the D.E. and deposits it on a grid. The D.E. then becomes the filter medium.

Dead spot Usually refers to a spot or location in a pool or spa where water circulation is poor or non-existent.

Decant To draw off the liquid from a container, basin or tank without stirring up the sediment in the bottom. The opposite of a slurry.

Dechlor or dechlorinate – also called chlorine neutralizer The process of adding a chemical to the water to remove the residual chlorine. Chemicals use for this are sodium thiosulfate, sodium bisulfite, sodium metabisulfite, sodium sulfite, hydrogen peroxide and Vitamin C.

Defoamer – also called anti-foam – A chemical added to the water to make the suds or foam go away. These products do not remove the source of the sudsing. Most often, the water must be drained and refilled to remove the soaps, oils and other causes of foaming. Shocking, superchlorination, clarifiers and enzymes may help remove causes.

Diameter The length of a straight line measured through the center of a circle from one side to the other.

Diatomaceous earth – also called D.E.– A white powder composed of fossilized skeletons of one-celled organisms called diatoms. The skeletons are porous and have microscopic spaces. The powder is added through the skimmer and deposits itself on a grid. The powder then becomes the filter medium.

Diatomaceous earth filter – also called a D.E. filter – A filter designed to use diatomaceous earth (D.E.) as the filter medium. The D.E. is added through the skimmer with the pump on which takes the D.E. and deposits it on a grid. The D.E. then becomes the filter medium.

Dichlor Common name for sodium dichloro-s-triazinetrione or the new term sodium dichloroisocyanurate. A fast-dissolving chlorine compound containing sodium, chlorine and cyanuric acid (stabilizer or conditioner). It has a neutral pH (pH 6.8) and is quick dissolving so it can be used for regular chlorination or superchlorination. Two types are sold. The anhydrous version that provides 62 percent available chlorine and is more dangerous to store and handle, and the dihydrate (Leslie’s Chlor Brite®) which has 56 percent available chlorine and is much safer to store and handle.

Diffuser A porous plate, tube or other device through which air is forced and divided into minute bubbles for diffusion in the water. A diffuser can also be an overdrain on a sand filter. A diffuser is also used on a closed-face impeller on a pump to concentrate water flow to the center of the impeller.

Discolored water Usually refers to water that has taken on a color from dissolved minerals, metals or from algae. Iron in water will turn water red or brown. Copper in water will turn water green or turquoise. Algae can make water look green, brown, blue or black.

Disinfect Means to kill all pathogenic (disease-causing) organisms. In drinking water it means a 99% kill of organisms compared to purification which is a 100% kill.

Dissolve The separation into component parts creating a process of solid particles mixing with a liquid and then taking on the appearance of the liquid. Like mixing sugar into water.

Dissolved solids – also called TDS or Total Dissolved Solids – A measure of the total amount of dissolved matter in water. Examples are calcium, magnesium, carbonates, bicarbonates, sodium, chlorides and metals. High levels can cause corrosion, colored water or salty taste. Maximum level usually 2500 ppm for pools. Maximum level for spas, 1500 ppm over starting level.

Distilled water Water formed by the condensation of steam or water vapor.

Diverter valve A plumbing fitting used to change the direction or re-direct the flow of water. Some diverter valves are used on pool/spa combination to allow the use of the spa and then switch the flow back to the pool. A brand name diverter valve is called an Ortega valve which is sometimes used to describe a diverter valve.

DPD Chemically, N,N-diethyl-p-phenylenediamine. An indicator reagent used for the determination of free and total chlorine, bromine, ozone and other oxidizers in water. Better than using OTO for chlorine because it measures free chlorine.

Drain Usually refers to a plumbing fitting installed on the suction side of the pump in pools, spas and hot tubs. Sometimes called the main drain and is located in the deepest part of the pool, spa or hot tub. It is not a drain such as a drain on a kitchen sink. Main drains do not allow the water to drain to waste but rather connect to the pump for circulation and filtration.

Dry acid See sodium bisulfate.

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