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Swimming Pool and Spa Terms


ALKALINITY Also called the buffering capacity of the water. It is the waters resistance to change in pH. Low total alkalinity causes metal corrosion, plaster etching and eye irritation. High total alkalinity causes scale formation, poor chlorine efficiency and eye irritation.

AVAILABLE OR RESIDUAL CHLORINE The amount of chlorine, both free and combined in the pool water that is available to sanitize or disinfect the water.

BAKING SODA Chemically called Bi-sodium carbonate. It is a white powder used to raise the pH and raise the total alkalinity

BROMINE A common name for a chemical compound containing bromine that is used as
a disinfectant to destroy bacteria and algae in swimming pools and spas.

BTU Abbreviation for British Thermal Unit

CALCIUM HYPO CHLORITE A compound of chlorine and calcium used as a disinfectant. It is available as a white granular material usually used for super chlorination, (WHITE PLASTER POOLS ONLY) or it is available as tablets used in a feeder for regular chlorinating. It usually contains 65% available chlorine.

CALCIUM HARDNESS The calcium content of the water. Calcium hardness is sometimes confused with the terms water hardness and total hardness. Too little calcium hardness and the water is corrosive. Too much calcium hardness and the water is scale forming. One of the basic water tests necessary to determine water balance. Minimum level is 150 ppm. Ideal range is 200 to 400 ppm.

CARTRIDGE FILTER A pool or spa water filter that uses an element made of paper or polyester.

CHLORINE NEUTRALIZER A chemical used to RENDER chlorine USE less. Used in test kits to counteract the bleaching effect of the chlorine or bromine in order to increase the accuracy of water tests.

CHLORINE A term used to describe any type of chlorine compound used as a disinfectant in swimming pool and spa water or to kill, destroy or control bacteria and algae. 

CLARIFIER A chemical compound used to gather (coagulate) or to precipitate suspended particles so they may be removed by vacuuming or filtration.

COPPER Corrosive water caused by misuse of chemicals, improper water balance, or placing tri-chlor tablets in the skimmer can cause copper to be dissolved from the equipment or plumbing and LEAVE on YOUR hair, fingernails or pool walls. High levels of copper also cause green water.

SOLAR COVER A cover that, when placed on the waters surface of a pool, spa or hot tub, increases the water temperature by absorption and transmission of solar radiation; reduces evaporation

CYUANURIC ACID Also called conditioner and stabilizer. It protects chlorine in the water from being destroyed by sunlight.  Too much does not slow down chlorine activity or effectiveness. Does not protect bromine from sunlight.

D. E. FILTER Diatomaceous Earth Filter - A filter designed to use diatomaceous earth. The D.E. is added through the skimmer with the POOL pump on, which takes the D.E. and deposits it on a grid.

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. 

DI-CHLOR A fast- dissolving chlorine compound containing chlorine and Cyuanuric acid (stabilizer or conditioner). It has a neutral pH and is quick-dissolving, so it can be used for regular chlorinating or super-chlorination

DRY ACID Chemically, sodium bisulfate. A dry white crystal that produces acid when added to water. It is used for lowering pH and total alkalinity.
Safer to handle than Muriatic acid

FREE CHLORINE The amount of free chlorine in the pool or spa water that is available to sanitize or disinfect the water. Sometimes called residual or available chlorine

GROUND-FAULT CIRCUIT INTERRUPTER -GFCI Ground-fault circuit-interrupter A device intended to protect people. It interrupts the electrical circuit whenever it detects the presence of excess electrical current going to ground

HYDROGEN PEROXIDE An unstable, colorless, heavy liquid used as a bleach in industry and as an antiseptic in households. It is used as an oxidizing agent in pools and spas
IRON Iron in water causes the water to be brown or green colored. This can be controlled by the addition of a sequestering agent or a chelating agent.

LIQUID CHLORINE A sodium hypo chlorite solution. Usually provides 10 to 12% available chlorine; has a pH of 13 and requires that small amounts of acid be added to the pool to neutralize the high pH.

LITHIUM HYPO-CHLORITE A dry, granular chlorinating compound with an available chlorine content of 35%. It is fast-dissolving and can be used to super chlorinate vinyl-liner pools, painted pools or fiberglass pools as well as spas and hot tubs.

MURIATIC ACID(1/3 hydrochloric acid) - Also called liquid acid An acid used to reduce the pH and alkalinity levels in pool water. It is also used in acid washing, a process that removes stains and scale from pool plaster.

NEUTRALIZER A chemical used to make chlorine or bromine harmless. Used in test kits to counteract the bleaching effect of the chlorine or bromine in order to increase the accuracy of pool water tests. Sold as chlorine and
bromine neutralizer, it is used to destroy excessive amounts of chlorine or bromine, so the high levels will not affect swimmers.

NON-CHLORINE SHOCK A term given to a class of chemical compounds that are used to oxidize or shock the water (destroy ammonia, nitrogen and swimmer waste). They contain no chlorine or bromine and do not kill living organisms. Swimmers may re-enter the water in only 15 minutes after adding a non-chlorine shock

OXIDIZER A non-chlorine shocking compound that removes or destroys built-up contaminants and chloramines in pool water without raising chlorine levels as required when "super-chlorinating."

OZONATOR It is used for oxidation of water contaminants.

pH Potential Hydrogen - Indicates the level of acidity or alkalinity of water on a scale ranging from 0-15. A low pH causes etched plaster, metal corrosion and eye irritation. A high pH causes scale formation, chlorine inefficiency and eye irritation. The ideal range for pH in swimming pools is 7.4 to 7.6

SAND FILTER a type of filter media composed of hard, sharp silica, quartz or similar particles with proper grading for size and uniformity. The most common of filter media composed of hard, sharp silica, quartz or similar grade used is No. 20 in sand filters

SCALE precipitation that forms on surfaces in contact with water when the calcium hardness, pH or total alkalinity levels are too high. Results from chemically unbalanced pool and spa water. Scale may appear as gray, white or dark streaks on the plaster, fiberglass or vinyl. It may also appear as a hard crust around the tile.

SODA ASH A chemical used to raise pH in pool and spa water.

SODIUM BISULFATE A chemical used to lower the pH and total alkalinity. 2 1/2 lb. of dry acid are equal to 1 quart of Muriatic acid.

SODIUM CARBONATE A chemical used to raise the pH in pool and spa water.

SODIUM DI-CHLOR A fast-dissolving, granular, stabilized organic chlorine compound. Used for regular as well as super-chlorination. Contains an ingredient (Cyuanuric acid or stabilizer) that prevents the chlorine from being destroyed by the UV rays of the sun, for use in vinyl-liner, painted or fiberglass pools and acrylic or fiberglass spas.

SODIUM HYPO CHLORITE Liquid chlorine. 10% to 12% for swimming pools

SODIUM THIOSULFATE A chemical used to neutralize-chlorine

TRI-CHLOR 90%+ available chlorine -(stabilized) A slow-dissolving, tabulated or granular, stabilized organic chlorine compound provide- 90% available chlorine. Used for regular chlorinating but must be dispensed using a float feeder or an in-line feeder . Tri-Chlor contains an ingredient  Cyuanuric acid or stabilizer that prevents the chlorine from being destroyed by the ultraviolet rays. Very acidic.

SOLAR COVER A cover that, when placed on the waters surface of a pool, spa or hot tub, increases the water temperature by absorption and transmission of solar radiation; prevents debris from entering the water.

STABILIZED CHLORINE Protects the chlorine from the degrading from sunlight. Most common types are sodium di-chlor and tri-chlor. The granular form is di-chlor which is fast-dissolving and can be used for regular chlorinating or super-chlorination by broadcasting into the pool or spa. Tablet or stick form is tri-chlor, used in a chlorine feeder for regular chlorinating only.

STAIN REMOVER Also called sequestering or chelating agent A chemical that will combine with dissolved metals in the water to prevent the metals from causing stains. May also be a used to remove dissolved metals from water.

SUPER CHLORINATE Adding an extra large dose of chlorine. This level of chlorine is required to destroy all of the combined chlorine in the water. This is called breakpoint.

TOTAL DISSOLVED SOLIDS  TDS Measure of the total amount of dissolved material in the water. Every time chemicals are added, TDS LEVEL WILL RISE. Maximum amount in pools is 2500 ppm. Maximum in spas is 1500 over starting TDS. The only way to effectively lower TDS is to drain part or all of the water and replace it with fresh water