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CYANURIC ACID: A granular chemical added to the pool water which provides a shield to chlorine for protection from UV radiation, which disrupts the molecule, destroying its sanitizing ability.
DIATOMACEOUS EARTH: The filtering medium of the DE filter, this dry powder is the fossilized remains of the ancient diatoms, a hard shelled form of algae. Found as a sedimentary rock that is easily broken down into a fine powder.
DIATOMACEOUS EARTH FILTER: A filter tank that features fabric covered grids which hold DE powder up against the flow of the water in order to filter out dirt and impurities as fine as 1 micron.
DICHLORO-S-TRIAZINETRIONE: A chemical compound. It is an oxidizer used to make bacteriocide, algicide, and cleaning agents. Reacts with water to form hypochlorous acid, which is related to bleach.
DISINFECTANT: Chemicals or processes which work to destroy vegetative forms of microorganisms and other contaminants. Examples are chlorine, bromine, Soft-Swim, and ionizers; also included are copper and silver algaecides.
DIVERTER VALVE: Used in a twin port skimmer, a diverter allows the operator to manipulate the amount of flow from the main drain and skimmer to the pump.
DPD: A method of testing for chlorine levels in the pool water. Unlike OTO, DPD testing allows determination of total and free available chlorine levels which through subtraction gives us combined levels.
DRAIN: Also called the "main drain," this plumbing fitting is the start of one suction line to the pump and is usually situated at or near the center bottom of the pool.
DRY ACID: Sodium bisulfate, a granular form of acid used to lower pH and alkalinity in the water. It is safer and less caustic than muriatic acid. Usually available as a "pH decreaser."
EFFICACY: The power to produce an effect. Chlorine's efficacy is affected by many factors, including the sun, water balance, and the water's chlorine demand.
EFFLUENT: The water that flows out of the pump on its way through the filter, heating, treating equipment, and then returning to the pool. Also known as the pressure side.
ELBOW: A 90 or 45 degree plumbing fitting. Used where your pipes take a turn
ELECTROLYSIS: A method of separating chemically bonded elements and compounds by passing an electric current through them.
ENZYMES: Used in swimming pool formulations designed to break down and digest oils in a pool or spa similar to the way enzymes are used in oil spill clean-up efforts.
FILL WATER: Used in filling or adding to the water level. Whether from the hose or from a well, your fill water brings its own chemical make up and water balance (or lack thereof).
FILTER: A device used to remove particles suspended in the water by pumping water through a porous substance or material.
FILTER ELEMENT: A device inside a filter tank designed to entrap solids and direct water through a manifold system to exit the filter. Cartridge filter elements and DE filter grids are two examples.
FILTER MEDIUM: A finely graded material such as sand, diatomaceous earth, polyester fabric, or anthracite coal that removes suspended particles from water passing through it.
FILTRATION RATE: The rate of water pumped through a filter, in gallons per minute (gpm).
FILM-X: A compound of citric acid used in cleaning plaster and other pool areas. Safe replacement for muriatic acid.
FOAMING: A term used to describe surface foam on your water, esp. in spas/hot tubs. Foaming is caused by high TDS levels working in combination with soft water and oils. Certain low grade algaecides can foam when added to pool or spa. Use enzymes for foam control.
FLOCCULENT: A chemical (such as alum) that used to combined suspended particulates in your pool water (cloudy water) to clump together and settle to the bottom of the pool where they can be easily vacuumed to waste.