Glossary of Terms

ACID: A sour chemical substance that releases hydrogen ions with the ability to dissolve metals, neutralize alkaline materials and to combine with bases to form salts. Acid is used to lower (decrease) pH and total alkalinity of swimming pool and spa water. Examples are muriatic acid (hydrochloric) and dry acid (sodium bisulfate). All liquids with a pH lower than 7.0 are acidic or acid.

AGGLOMERATION: The gathering of fine, suspended matter in water into “flocs” or larger masses that then can settle and be filtered from the water.

ALGAE: Microscopic plant-like organisms that contain chlorophyll. Algae are nourished by carbon and use sunlight to carry out photosynthesis. They are introduced by rain or wind and grow in colonies producing nuisance masses. Algae are not disease-causing but they can harbor bacteria and they are slippery. There are 21,000 known species of algae. The most common pool types are black, blue-green, green and yellow or mustard. Pink or red colored algae-like organisms exist but are bacteria and not algae. Maintaining proper sanitizer levels, shocking and superchlorination will prevent their occurrence.

ALGAECIDE: (also algicide) A natural or synthetic chemical designed to kill destroy or control algae.

ALGAESTAT: (also algistat) Any chemical or substance that inhibits the growth of algae.

ALKALI: (also called base) A class of compounds which will react with an acid to give a salt. A substance that creates a bitter taste and a slippery feel when dissolved in water. An alkali has a pH greater than 7.0 and is the opposite of an acid. Alkalis may include the soluble hydroxide, carbonate and bicarbonate salts of calcium, magnesium, potassium and sodium. A reaction between an acid and a base is called neutralization.

ALKALINITY: (also more commonly called total alkalinity) A measure of the pH-buffering capacity of water. Also defined as the water's resistance to change in pH. Composed of the hydroxides, carbonates and bicarbonates in the water expressed in parts per million (ppm) or milligrams per liter (mg/L). One of the basic water tests necessary to determine water balance. The ideal range is from 60 parts per million (ppm) to 140 ppm.

AMMONIA: Introduced into the water by swimmers as waste (perspiration or urine). Quickly forms foul-smelling, body-irritating chloramines - a disabled, less effective form of chlorine. See chloramines or combined chlorine.

ANTI-FOAM: A chemical added to the water to remove suds or foam. These products do not alleviate 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 the causes.

ANTI-SCALANT: A chemical that inhibits or delays precipitation and subsequent scale formation.

AVAILABLE CHLORINE: The amount of chlorine, both free and combined, in the pool water that is available to sanitize or disinfect the water. Sometimes called residual chlorine.

BACKWASH: The process of thoroughly cleaning the filter by reversing the flow of water through it with the dirt and rinse water going to waste.

BACKWASH RATE: The rate of flow through the filter media during the backwash cycle, measured in gallons per minute per square foot (GPM/Sq. Ft.).

BACTERICIDE: A chemical or element that kills destroys or controls bacteria.

BACTERIOSTAT: A substance that prevents or retards bacteria growth.

BALANCED WATER: The correct ratio of mineral content, pH and alkalinity levels that prevents water from being corrosive or scale forming.

BIOCIDE: Any substance or medium having the energy to destroy bacteria. Any substance or chemical that kills or inhibits the growth or microorganisms such as fungi, bacteria, molds and slimes.

BLACK ALGAE: A stubborn strain of algae that grows in pools and spas. It can be difficult to remove. See algae.

BLEACH: This term usually refers to liquid chlorine (sodium hypochlorite, NaOCl, 10-percent to 12-percent chlorine by weight). It is the same chemical used in laundry bleach but pool chlorine is 12-percent available chlorine while laundry bleach is about 5-percent to 6-percent available chlorine. A gallon of liquid chlorine contains about 1 pound of pure chlorine or is equivalent to 1 pound of gas chlorine.

BODY OIL: The term used to describe oil from or on our bodies that gets into the water. Sometimes it refers to sun tan oil or lotion.

BROMAMINES: By-products formed when bromine reacts with swimmer waste (perspiration or urine), nitrogen or fertilizer. Bromamines are active disinfectants and do not smell, although, high levels are body irritants. Bromamines are removed by superchlorination or shock treatment.

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. Available as a tablet or as sodium bromide, a granular salt.

BROMINE TABLETS: Common name for two chemical compounds containing bromine. They are used as disinfectants to destroy bacteria and algae. A separate oxidizer must be used to destroy swimmer waste.

BROMINATOR: A mechanical or electrical device for dispensing bromine at a controlled rate. Most often a canister or floater filled with tablets of bromine.

BROWN ALGAE: A particularly hardy kind of algae that can look brown but is actually what is called yellow or

CALCIUM: The presence of calcium in water is a factor contributing to the formation of scale and is a means of identifying hard water.

CALCIUM CARBONATE: Crystalline compounds formed in swimming pool and spa water when the calcium, pH and total alkalinity levels are too high. Once formed, the crystals adhere to the plumbing, equipment, pool walls and pool bottom. These crystals are better known as scale.

CALCIUM CHLORIDE: A soluble white salt used to raise the calcium or total hardness level in the pool or spa water.

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 forms scale. One of the basic water tests necessary to determine water balance. Minimum level 150 parts per million (ppm). Ideal range is 200 ppm to 400 ppm.

CALCIUM HYPOCHLORITE: A compound of chlorine and calcium used as a disinfectant, sanitizer, bactericide, algaecide and oxidizer in swimming pool and spa water. It is available as a white granular material usually used for superchlorination or it is available as tablets used in a feeder for regular chlorination. It usually contains 65-percent available chlorine but is available as 70 percent and 75 percent also. Often referred to as cal-hypo.

CARTRIDGE: A replaceable porous element made of paper or polyester used as the filter medium in cartridge filters.

CARTRIDGE FILTER: A pool or spa water filter that uses a replaceable porous element made of paper or polyester as its removal system.

CHELATE: Pronounced KEY-late. Also called sequester. It is the process of preventing metals in the water from combining with other components in the water to form colored precipitates that stain pool walls and bottoms or produce colored water.

CHELATED COPPER: Copper algaecides that contain a special ingredient to prevent the copper from staining pool walls and bottoms or producing colored water.

CHEMICAL FEEDER: Any of several types of devices that dispense chemicals into the pool or spa water at a predetermined rate. Some dispense chlorine or bromine while others dispense pH-adjusting chemicals.

CHLORAMINES: Undesirable, foul-smelling, body-irritating compounds formed when insufficient levels of free available chlorine react with ammonia and other nitrogen-containing compounds (swimmer and bather waste, fertilizer, perspiration, urine, etc.). Chloramines are still disinfectants but they are a much weaker, ineffective form of chlorine. Chloramines are removed by super-chlorination or shock treatment.

CHLORIDE: The ionic, non-killing form of chlorine. When chlorine in water is reduced or is used up, it becomes chloride ion in water.

CHLORINATOR: A mechanical or electrical device for dispensing chlorine at a controlled rate. Most often a canister or floater filled with tablets of chlorine.

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. In addition, chlorine oxidizes ammonia and nitrogen compounds (swimmer and bather waste).

CHLORINE DEMAND: The amount of chlorine necessary to oxidize all organic matter (bacteria, algae, chloramines, ammonia and nitrogen compounds) in the pool or spa water.

CHLORINE ENHANCER: A chemical compound that, when used in conjunction with chlorine, makes the chlorine perform better as an algaecide.

CHLORINE NEUTRALIZER: A chemical solution used to make chlorine 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. Chemicals used for this are sodium thiosulfate, sodium bisulfite, sodium metabisulfite, sodium sulfite, hydrogen peroxide and Vitamin C.

CHLORINE RESIDUAL: The amount of chlorine left in the pool or spa water after the chlorine demand has been satisfied.

CLARIFIER: A chemical compound used to gather or to precipitate suspended particles so they may be removed by vacuuming or filtration. There are two types: inorganic salts of aluminum (alum) or water-soluble organic polyelectrolytes. Often referred to as a coagulant or flocculent.

CLARITY: The degree of transparency of the water.

CLOUDY WATER: The visible effect in water created by material in suspension - also called turbidity. Adding a clarifier will coagulate the particles and make the filter more efficient.

COAGULANT: An organic polyelectrolyte used to gather (coagulate) suspended particles in the water.

COMBINED CHLORINE: Undesirable, foul-smelling, body-irritating compounds formed when insufficient levels of free available chlorine react with ammonia and other nitrogen-containing compounds (swimmer and bather waste, fertilizer, perspiration, urine, etc.). Combined chlorine is still a disinfectant but it is a much weaker, ineffective form of chlorine.

CONDITIONER: See cyanuric acid.

COPING: The cap or top lip on the pool or spa wall that provides a finishing edge around the pool or spa. It can be formed, cast in place, precast or pre-fabricated of extruded aluminum or rigid vinyl. It may also be part of the system that secures a vinyl liner to the top of the pool wall.

COPPER ALGAECIDE: A chemical compound that contains the element copper. Copper sulfate was one of the original copper algaecides. Too much copper in the water can cause green-colored stains. Newer copper algaecides contain an ingredient that prevents the copper from staining but does not affect copper's ability to kill algae. These special copper algaecides are called chelated copper algaecides.

COPPER SULFATE: A chemical prepared from copper and sulfuric acid. It is one of the oldest algaecides available. It is also called blue vitriol, blue copperas, bluestone and cupric sulfate.

CORROSION: The etching, pitting or eating away of the pool or spa vessel or equipment. Caused by improper water balance, misuse of acid or acidic products or from "soft" water.

HARD TOP COVER - A cover used on pools, spas and hot tubs that rests on the lip (coping) of the pool or spa deck, not a flotation cover, used as a barrier to swimmers and bathers, for maintenance and thermal protection.

WINTER COVER - A cover that is secured around the perimeter of a pool, spa or hot tub and provides a barrier to bathers and debris when closed for the season.

SOLAR COVER - A cover that, when placed on the water's surface of a pool, spa or hot tub, increases the water temperature by absorption and transmission of solar radiation, reduces evaporation and prevents wind-borne debris from entering the water.

CYANURIC ACID: (also known as conditioner and stabilizer) It protects chlorine in the water from being destroyed by sunlight. Minimum level 30 parts per million. Too much does not slow down chlorine activity or effectiveness. It does not protect bromine from sunlight.

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 when the pump is on. This deposits the D.E. on a grid, where it then becomes the filter medium.

DECHLOR OR DECHLORINATE: (also called chlorine neutralizer) The process of adding a chemical to the water to remove the residual chlorine. Chemicals used 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.

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: A fast-dissolving chlorine compound containing sodium, chlorine and cyanuric acid (stabilizer or conditioner). It has a nearly 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 provides 62-percent available chlorine and is more dangerous to store and handle. The dihydrate, which has 56-percent available chlorine, is much safer to store and handle.

ETCHING: Corrosion of the surface of a vessel, plumbing, equipment or fixtures. Plaster etching is caused by corrosive or aggressive water, usually because the pH and alkalinity are too low.

FIBERGLASS: Fine-spun filaments of glass which are available in a rope or mat form. When used in a process with polyester resins, catalysts and hardeners, fiberglass can be formed or molded into pools, spas and related shapes.

FILL WATER: (also called makeup water) Water added to a pool or spa to replace water lost due to evaporation, splash out or drag out.

FILTER: A device that removes undissolved or suspended particles from water by recirculating the water through a porous substance (a filter medium or element). The three types of filters used in pools and spas are sand, cartridge and D.E. (diatomaceous earth).

FILTER AID: A chemical compound added to the water or added to the filter that allows the existing filter to become more efficient. Examples are alum, water clarifiers and D.E. (diatomaceous earth).

FILTER CYCLE: The operating time between cleaning or backwashing cycles of a filter. Also, the amount of time the filter has water flowing through it each day expressed in hours.

FILTER ELEMENT: A device within a filter tank designed to trap suspended solids as water from the pool or spa is flowing through it.

FILTER MEDIUM: In essence, the material used in the filter to trap suspended dirt particles as the water is flowing through it. The polyester or paper used in making a cartridge filter element. The sand used in a sand filter. The D.E. (diatomaceous earth) used in a D.E. filter.

FILTRATION RATE: The rate at which the water is traveling through the filter expressed in gallons per minute (gpm) per square foot of filter area.

FLOATER: A chemical feeder whereby the chemical is placed in a container and the container is allowed to float around the pool dispensing the chemical. The chemical dissolves in the floater and is released into the water. Most often these are used for chlorine or bromine.

FLOC: The clump or tuft formed when suspended particles combine with a flocculating agent.

FLOCCULATING AGENT: (also flocculant) A chemical substance or compound that promotes the combination, agglomeration, aggregation or coagulation of suspended particles in the water.

FLOCCULATION: The combination, agglomeration, aggregation or coagulation of suspended particles in such a way that they form small clumps or tufts (called floc).

FOAM: A froth of bubbles on the surface of the water. Usually caused by soap, oil, deodorant, hair spray, sun tan oil, etc. that is shed into the water as swimmers enter.

FREE AVAILABLE CHLORINE (FAC): The amount of free chlorine in the pool or spa water that is available to sanitize or disinfect the water. FAC is sometimes called residual or available chlorine.

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

GAS CHLORINE: A chemical element used as a sanitizer and disinfectant in swimming pool water. The greenish gas is compressed and becomes a liquid under pressure. It is 2.5 times heavier than air and is highly toxic to humans if released.

GUNITE: A mixture of cement and sand sprayed onto contoured and supported surfaces to build a pool. Gunite is mixed and pumped to the site dry and water is added at point of application. Plaster is usually applied over the gunite.

HAIR & LINT STRAINER: Usually a basket before the pump that is design to catch and prevent hair, lint and other small material from entering the pump where it may damage the impeller.

HALOGENS: The chemical elements either individually or collectively that constitute Group VIIA of the periodic table: namely, fluorine, chlorine, bromine iodine and astatine. Of these, only chlorine and bromine are used as disinfectant and sanitizers in pool and spas.

HAND SKIMMER: A screen attached to a frame which can be connected to a telepole to remove large floating debris such as leaves and bugs from the water's surface.

HARD WATER: Drinking water term that indicates water that contains one grain per gallon - 17.1 parts per million (ppm) or milligrams per liter (mg/L) or higher of total hardness. The ideal range of hardness for pools and spas is 200 ppm to 400 ppm.

HARDNESS: The amount of calcium and magnesium dissolved in the water. "Water" or "total" hardness refers to the total of the magnesium and calcium dissolved in the water. Calcium hardness refers to just the calcium. Measured by a test kit and expressed as parts per million (ppm). Proper range is 200 ppm to 400 ppm.

HARDNESS INCREASER: A chemical used to increase calcium or water hardness. It is usually calcium chloride.

HEATER: A fossil-fueled, electric or solar device used to heat the water of a pool, spa or hot tub.

HYDROJET: A fitting in the pool or spa on the water return line from the equipment that blends or mixes air and water creating a high velocity, turbulent stream of air-enriched water.

IDEAL LEVEL OR RANGE: The universally accepted ranges for the chemical parameters for swimming pool or spa water. For instance, the ideal pH range is 7.4 to 7.6; the ideal chlorine level is 1.5 parts per million (ppm) to 3.0 ppm; the ideal total alkalinity is 80 ppm to 140 ppm depending on the sanitizer being used; the ideal hardness level is 200ppm to 400 ppm.

IONIZER: A water-sanitation device that uses electricity to generate metal ions which are dispersed in the water. It works by passing a low-voltage, DC current through a set of metallic (usually copper and silver) electrodes placed in line with the circulation equipment. The copper is an algaecide while the silver is a bactericide. This process does not remove swimmer waste.

JET: (also called a hydrojet or hydrotherapy jet) A fitting in the pool or spa on the water return line from the equipment that blends or mixes air and water creating a high velocity, turbulent stream of air-enriched water.

LINER: (also vinyl liner) The vinyl membrane that acts as the container to hold or contain the water in a swimming pool.

LIQUID CHLORINE: Sodium hypochlorite solution, chemical formula usually provides 10 percent to 12 percent available chlorine; has a pH of 13 and requires that small amounts of acid be added to the pool to neutralize the high pH. Good for regular chlorination and superchlorination. It is the same chemical used for household or laundry bleach except that laundry bleach is about 5.6-percent available chlorine. One gallon of liquid chlorine 12.5 percent is equal to about one pound of gas chlorine.

LITHIUM HYPOCHLORITE: A dry, granular chlorinating compound with an available chlorine content of 35 percent. It is rapid dissolving and should be used to superchlorinate vinyl-liner pools, painted pools or fiberglass pools as well as spas and hot tubs.

MAGNESIUM HARDNESS: A measure of the amount of magnesium dissolved in the water. It is part of total or water hardness. It also causes scale if levels are too high. In tap water, magnesium hardness is about 25 percent of the total hardness and calcium is about 75 percent.

MAIN DRAIN: Usually refers to a plumbing fitting installed on the suction side of the pump in pools, spas and hot tubs. Sometimes called the drain, it is located in the deepest part of the pool, spa or hot tub. The Main Drain is unique in that it does not allow the water to drain to waste but rather connect to the pump for circulation and filtration.

MAKE-UP WATER: Sometimes called "tap" or "refill" water. It is the water used to replace water lost to evaporation, splash out, leaks or swimmer drag out in the pool.

MEDIA: A selected group of materials used in filters and filter devices to form barriers to the passage of certain solids or molecules that are suspended or dissolved in water. Media is the plural form of medium and refers to more than one type of barrier material. In the pool and spa industry, filters use either sand, polyester or diatomaceous earth (D.E.) as the media.

MSDS: Abbreviation for Material Safety Data Sheet, an informative fact sheet provided by companies that make and distribute hazardous substances. As part of the Worker Right to Know Law, an MSDS must be available for each substance and mixtures of hazardous substances.

MURIATIC 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.

MUSTARD ALGAE: A particularly hardy form of algae that is yellow colored. See algae.

NEUTRALIZER: A chemical solution 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. The most common ones are sodium thiosulfate, sodium sulfite, sodium metabisulfite, hydrogen peroxide and vitamin C.

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. Examples are monopersulfates, hydrogen peroxide and percarbonates.

NSPI: Abbreviation for the National Spa & Pool Institute.

ORGANIC CHLORAMINES: Chloramines formed from the combination of chlorine and organic ammonia or nitrogen (swimmer waste, perspiration, urine, sweat, saliva, etc.) these are not considered disinfectants like inorganic chloramines.

OXIDATION: To rid the water of ammonia, nitrogen compounds and swimmer waste (organic compounds). These organic compounds disable chlorine, are body irritants and have a foul smell. Removal is accomplished by superchlorination or by shock treating with a non-chlorine oxidizer.

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 "superchlorinating."

PART PER MILLION: Abbreviated as ppm. It is a "weight-to-weight" expression. It means one part in one million parts, such as, 1 pound of chlorine in 1 million pounds of water or 119,904 gallons.

pH: A term used to indicate the level of acidity or alkalinity of pool water. Too low pH causes etched plaster, metal corrosion and eye irritation. Too high pH causes scale formation, poor chlorine efficiency and eye irritation. Proper range for pH in swimming pools is 7.4 to 7.6. It is always written with a lower case "p" and a capital "H."

pH DECREASER: A chemical that decreases or lowers the pH of the water. Muriatic acid, dry acid and sodium bisulfate are examples.

pH INCREASER: A chemical that increases the pH of the water. Soda ash, sodium sesquicarbonate and sodium bicarbonate are examples of pH increasers.

pH METER: A sensitive volt meter used to measure pH via an electrode placed in the water.

PLASTER: A mixture of white cement and white marble dust used as an interior finish which can be tinted, colored or left white, applied to the gunite or shotcrete of a pool or spa.

PUMP: A mechanical device, usually powered by an electric motor, which causes hydraulic flow and pressure for the purpose of filtration, heating and circulation of pool and spa water. Typically, a centrifugal pump is used for pools, spas and hot tubs.

QUAT: See quaternary ammonium compounds.

QUATERNARY AMMONIUM COMPOUNDS: (also called quats) A type of organic compound in which the molecular structure includes a central nitrogen atom joined by four organic groups as well as to an acid radical. Cationic quaternary ammonium compounds adsorb on the cell walls of microbes and algae and react chemically with the negative charges carried by the cell walls. These chemical compounds of ammonia are used as algaecides and algaestats.

REAGENTS: The chemical agents, dyes, indicators or titrants used in testing various aspects of water quality.

RESIDUAL BROMINE: The amount of measurable bromine remaining after treating the water with bromine. The amount of bromine left in the pool or spa water after the bromine demand has been satisfied. Includes hypobromous acid (HOBr), hypobromite ion, free and total bromine and all combined bromine.

RESIDUAL CHLORINE: The amount of measurable chlorine remaining after treating the water with chlorine. The amount of chlorine left in the pool or spa water after the chlorine demand has been satisfied. Includes hypochlorous acid (HOCl), hypochlorite ion free and total chlorine and all combined chlorine.

SAND: Usually refers to the filter medium used by a sand filter. The grade most often specified by filter manufacturers is grade #20 with a particle size of 45 to 55 mm (millimeters).

SAND FILTER: A filter using sand or sand and gravel as the filter medium. The oldest (patented in 1790) method of improving water quality, generally using two layers of sand supported by an underbed layer of gravel.

SANITIZE: To render sanitary; to kill all living things including bacteria and algae. Similar to sterilize.

SCALE: The precipitate that forms on surfaces in contact with water when the calcium hardness, pH or total alkalinity levels are too high. This is the result of chemically unbalanced pool and spa water. Scale may appear as grey, white or dark streaks on the plaster, fiberglass or vinyl. It may also appear as a hard crust around the tile.

SCALE INHIBITOR: A chemical added to the water that prevents scale from forming.

SCUM: The extraneous or foreign matter which rises to the surface of the water and forms a layer or film there. It can also be a residue deposited on the tile or walls of the pool or spa. Sources of scum are soap, oil, deodorant, hair spray, sun tan lotion and various others.

SEQUESTERING AGENT: (also called chelating agent) A chemical that will combine with dissolved metals in the water to prevent the metals from coming out of solution (precipitating or causing stains). May also be a chemical that removes dissolved metals from water.

SHOCK TREAT: The practice of adding significant amounts of an oxidizing chemical (usually non-chlorine oxidizers such as sodium persulfate or potassium peroxymonosulfate) to the water to destroy ammonia and nitrogen compounds or swimmer waste. Shock treat used to mean superchlorinating to 10 parts per millions (ppm) to 20 ppm of free chlorine.

SHOTCRETE: A mixture of sand and cement sprayed onto contoured and supported surfaces to build a pool or spa. Plaster is applied over the shotcrete. Shotcrete is premixed and pumped wet to the construction site.

SILVER ALGAECIDE: Algaecides that have colloidal silver or silver ions as their active ingredient.

SKIMMER: A device installed through the wall of a pool or spa that is connected to the suction line of the pump that draws water and floating debris in from the surface of the water. The skimmer basket catches large debris while the filter traps smaller particles.

SKIMMER BASKET: A removable, slotted basket or strainer placed in the skimmer on the suction side of the pump, which is designed to trap floating debris in the water flow from the surface without causing much flow restriction.

SKIMMER WEIR: Part of a skimmer that adjusts automatically to small changes in water level to assure a continuous flow of water to the skimmer. The weir has the appearance of a small floating "door" on the side of the skimmer that faces the water over which water flows on its way to the skimmer.

SODIUM BICARBONATE: (baking soda or bicarb) Used to raise total alkalinity in pool and spa water with only a slight affect on the pH.

SODIUM BISULFATE: (dry acid) A chemical used to lower the pH and total alkalinity (2.5 pounds of dry acid are equal to 1 quart of muriatic acid).

SODIUM BORATE: See sodium tetraborate.

SODIUM BROMIDE: A salt of bromine, used to establish a bromide "bank" in pool and spa water prior to beginning the use of bromine tablets.

SODIUM CARBONATE: (common name - soda ash) A chemical used to raise the pH and total alkalinity in pool and spa water.

SODIUM DICHLOR: A fast-dissolving, granular, stabilized organic chlorine compound providing either 56-percent or 63-percent available chlorine. Used for regular as well as superchlorination. It also contains an ingredient (cyanuric acid or stabilizer) that prevents chlorine from being destroyed by the ultraviolet (UV) rays of the sun.

SODIUM HYPOCHLORITE: Good for regular chlorination and superchlorination. It is not recommended for spas and does not contain conditioner or stabilizer to protect it from sunlight, but it is protected if stabilizer or conditioner is already in the water. It usually provides 10-percent to 12-percent available chlorine (or about 1 pound of pure chlorine per gallon); has a pH of 13; and requires that small amounts of acid be added to the pool to neutralize the high pH.

SODIUM SESQUICARBONATE: A chemical mixture of equal parts of soda ash and sodium bicarbonate used to increase pH and total alkalinity in pool and spa water. It has a pH of 10.1.

SODIUM SULFITE: A chemical used to neutralize, de-chlorinate or debrominate pool and spa water.

SODIUM TETRABORATE PENTAHYDRATE: White crystals or powder used to scavenge from water and as a buffer which supplies alkalinity to water so pH can be more easily maintained.

SODIUM THIOSULFATE: A chemical used to neutralize, de-chlorinate or debrominate pool and spa water.

SOFT WATER: Water that has a very low calcium and magnesium content (water hardness) - usually means less than 100 parts per million (ppm) or 6 grains. Also includes water that has been processed through a water softener. Pools and spas should never be filled with soft water from a softener. Water with less than 100 ppm of hardness should be increased to a minimum of 150 ppm to 200 ppm using calcium chloride.

SOLAR COVER: A cover that when placed on the water's surface of a pool, spa or hot tub, increases the water temperature by absorption and transmission of solar radiation, reduces evaporation and prevents wind-borne debris from entering the water.

SOLAR HEATING SYSTEM: Usually panels or coils of plastic or metal through which water passes to increase the temperature from the sun's radiant heat.

SOURCE WATER: (also called "tap" water) The water used to fill or refill the pool or spa.

STABILIZED CHLORINE: A family of chlorine pool sanitizers that contain conditioner (cyanuric acid or isocyanuric acid) to protect the chlorine from the degrading ultraviolet (UV) rays in sunlight. Most common types are sodium dichlor and trichlor. Granular form is dichlor which is fast dissolving and can be used for regular chlorination or superchlorination by broadcasting into the pool or spa. Tablet or stick form is trichlor which is usually used in a chlorine feeder either the floating type or the in-line erosion type used for regular chlorination only.

STABILIZER: (also known as conditioner) See cyanuric acid.

STAIN: A discoloration or a colored deposit on the walls or bottom of a swimming pool or spa. Most often stains are metallic oxides, hydroxides, carbonates, sulfates, silicates and phosphates of such metals as iron, copper and manganese. They may appear as green, gray, brown or black.

STAIN INHIBITOR: See sequestering agent.

STERILIZE: To destroy or kill by any of several means all living microorganisms in water.

SUPERCHLORINATION: The practice of adding an extra large dose - 5 parts per million (ppm) to 10 ppm - of chlorine to the water to destroy ammonia, nitrogen and swimmer waste which can build up in the water. This level of chlorine is required to destroy all of the combined chlorine in the water, which is called break-point chlorination.

SUSPENDED SOLIDS: See TDS.

TAC: Abbreviation for Total Available Chlorine. It is the total amount of chlorine in the water and includes both free available chlorine and combined available chlorine.

TDS: (also called Total Dissolved Solids) A measure of the total amount of dissolved material in the water. It is comprised of the spent or carrier chemicals added every time chemicals are added as well as the hardness, alkalinity, chlorides, sodium, magnesium, calcium, etc. The maximum amount in a pool is 2,500 parts per million (ppm). Maximum for a spa is 1,500 over starting TDS. The only way to effectively lower TDS is to drain part or all of the water and replace it.

TELEPOLE: A long-handled aluminum pole designed to extend in length. Various pool-cleaning tools such as brushes or vacuums may be attached.

TEST KIT: An apparatus or device used to monitor specific chemical residuals, levels, constituents or demands in pool or spa water. Kits usually contain reagents, vials, titrants, color comparators and other materials needed to perform tests. The most common pool and spa water tests are: pH, total alkalinity, free available chlorine, water hardness, cyanuric acid, iron and copper.

TEST STRIPS: Small plastic strips with pads attached that have been impregnated with reagents that can be used to test pool water for residuals, levels, constituents or demands. The strips are usually dipped in the water and the resulting colors of the pads compared to a standard set of colors to determine concentration.

TITRATION: The method used to test for total alkalinity and water hardness in swimming pool and spa water. An indicator reagent is added to a sample and then another reagent (a titrant) is added until the sample changes color. The drops or amount of titrant used are equal to the concentration in parts per million.

TOTAL ALKALINITY: The total amount of alkaline materials present in the water, also called the buffering capacity of the water. It is the water's 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. The test measures for hydroxides, carbonates and bicarbonates.

TOTAL CHLORINE: (also Total Available Chlorine) The total amount of chlorine in the water. It includes both free available and combined chlorine.

TRICHLOR: A slow-dissolving, stabilized organic chlorine compound in tablet form that provides 90-percent available chlorine. Used for regular chlorination but must be dispensed using a floating feeder or an in-line feeder (chlorinator). Trichlor contains an ingredient (cyanuric acid or stabilizer) that prevents the chlorine from being destroyed by the ultraviolet (UV) rays of the sun. Trichlor has a pH of 2.8 and regular trichlor tabs should not be placed in the skimmer as the low pH will corrode the metal components in the equipment.

TURBIDITY: Cloudy condition of the water due to the presence of extremely fine particles in suspension that can not be trapped by the filter because they are too small. Adding a clarifier such as an organic polymer or alum will coagulate the particles and make the filter more efficient. Turbidity is measured with a Nephelometer and expressed in units of opaqueness called NTU (Nephelometer Turbidity Units).

VINYL LINER: The vinyl membrane that acts as the container to hold or contain the water.

WATER BALANCE: Water that has a pH of 7.4 to 7.6, a total alkalinity of 80 parts per million (ppm) to 140 ppm, calcium hardness of 200 ppm to 400 ppm, and a TDS of less than 2,500 ppm. The water is said to be "in balance" when the water is within these parameters.

WATER CLARIFIER: (also called coagulant or flocculent) A chemical compound used to gather (coagulate or agglomerate), or to precipitate suspended particles so they may be removed by vacuuming or filtration. There are two types: inorganic salts of aluminum (alum) and other metals or water-soluble organic polyelectrolytes.

WEIR: (also called skimmer weir) Part of a skimmer that adjusts automatically to small changes in water level to assure a continuous flow of water to the skimmer. The small floating "door" on the side of the skimmer that faces the water over which water flows on its way to the skimmer.

WINTER COVER: A cover that is secured around the perimeter of a pool, spa or hot tub that provides a barrier to bathers and debris when the pool, spa or hot tub is closed for the season.

WINTERIZING: The procedure for preparing the pool or spa for freezing weather. Includes chemical treatment and physical treatment to protect equipment and vessel - draining, anti-freeze, drain plugs, etc.

YELLOW ALGAE: A particularly hardy kind of algae that is yellow or mustard colored.