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Pool Terms Glossary
Acid – A sour chemical substance containing hydrogen with the ability to dissolve metals, neutralize alkaline materials and 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).
Acid Rain – Precipitation having an unusually low pH value (4.5 or lower) caused by absorption of air polluted by sulfur dioxide, carbon dioxide and nitrous oxide.
Air Blower – A mechanical device that forces air through holes in the floor, bubbler ring or hydrotherapy jets in a spa.
Air-Relief Valve – A brass or plastic, manually operated valve located at the top of a filter tank for relieving the pressure inside the filter and for removing the air inside the filter (called bleeding the filter). Sometimes called a pressure-relief valve.
Algae – Microscopic organisms exhibiting plant-like characteristics that contain chlorophyll. Algae are nourished by carbon dioxide (CO) and use sunlight to carry out photosynthesis. They are typically introduced by rain or wind and often grow exponentially in colonies producing masses. Algae are not disease-causing, but can harbor bacteria, and are often slippery. Estimates are there are between 21,000 to 30,000 known species of algae. The most common pool types are black, blue-green, green and mustard (yellow or brown). Pink or red-colored algae-like organisms exist but are often bacteria and not algae. Maintaining proper sanitizer levels, shocking and superchlorination will help prevent its occurrence.
AlgaecideAlso called algaecide – A natural or synthetic chemical designed to kill, destroy or control algae.
AlkalinityAlso more commonly called total alkalinity – A measure of the pH-buffering capacity of water. Also called the water’s resistance to change in pH. Composed of the hydroxides, carbonates and bicarbonates in the water. One of the basic water tests necessary to determine water balance.
Ammonia – Introduced into the water by swimmers as waste (perspiration or urine) or by other means. Quickly forms foul-smelling, body-irritating chloramines – a disabled, less-effective form of chlorine. See chloramines or combined chlorine.
Automatic Pool Cleaner – Also called a sweep, pool sweep - A pool maintenance system that will agitate or vacuum debris from the pool interior automatically. There are both suction based and pressure based sweeps. The best performing sweeps are pressure based and have a booster pump providing power for movement such as the Polaris 280
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.
Baking Soda – Chemically called sodium bicarbonate. It is a white powder used to raise the total alkalinity of pool or spa water without having much effect on pH.
Balanced Water – The correct ratio of mineral content and pH level that prevents the water from being corrosive or scale forming.
Bleach – This term usually refers to liquid chlorine (sodium hypochlorite 12% available chlorine). It is the same chemical used in laundry bleach.
Breakpoint Chlorination – The process of adding sufficient free available chlorine to completely oxidize all organic matter and ammonia or nitrogen compounds. The dosage is 10 times the combined chlorine value. All chlorine added after that point is free available chlorine.
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 treating.
BTU – Abbreviation for British Thermal Unit. The amount of heat necessary to raise 1 lb. of water 1 Fahrenheit.
Calcium Carbonate – Also known as scale - 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 bottom.
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 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.
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% available chlorine.
Cartridge Filter – A pool or spa water filter that uses a replaceable porous element made of paper or polyester.
Check Valve – A mechanical device in a pipe that permits the flow of water or air in one direction only.
Chelate – (pronounced KEY-late) – Also called sequester – It is the process of preventing metals in the water from combining with other components in water to form colored precipitates that stain the pool walls and bottom or produce colored water.
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 superchlorination or shock treating.
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 Enhancer – A chemical compound that when used in conjunction with chlorine makes the chlorine perform better as an algaecide.
Chlorine Generator – An electrical device that generates chlorine from a salt solution in a tank or from salt added to the pool water.
Chlorine Lock – This is a term that implies that an overabundance of cyanuric acid (stabilizer or conditioner) in the water would cause the chlorine to be all “locked up.” Opinions can vary tremendously on validity of this.
Chlorine Neutralizer – A chemical 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.
Clarity – The degree of transparency of 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 – Chemically, conditioner is cyanuric acid. It slows down the degradation of chlorine in the water by sunlight. A very minimum level is 10 ppm. Conditioner does not protect bromine from sunlight.
Copper – It is one of nature’s elements. It is also used for various parts of equipment and plumbing in swimming pools and spas. Corrosive water caused by misuse of chemicals or improper water balance can cause copper to be dissolved from the equipment or plumbing and deposit the precipitates on hair, fingernails or pool walls. High levels of copper also cause green water. Copper is also commonly used as a metal based algaecide.
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.
Cover, Winter – 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.
Cyanuric AcidAlso called conditioner and stabilizer – Chemically, conditioner is cyanuric acid. It protects chlorine in the water from being destroyed by sunlight. Minimum level is 10 ppm. Too much does not slow down chlorine activity or effectiveness. Does not protect bromine from sunlight.
Diatomaceous EarthAlso 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 with the pump on and deposits itself on a grid. The powder then becomes the filter medium.
Diatomaceous Earth FilterAlso 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 – The common name for sodium dichlor. A fast-dissolving chlorine compound containing chlorine and cyanuric acid (stabilizer or conditioner). It has a neutral pH and is quick-dissolving, so it can be used for regular chlorination or superchlorination.
Disinfect – To kill all pathogenic (disease-causing) organisms.
Dissolved SolidsAlso 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.
Diving Board – A recreational mechanism for entering a swimming pool, consisting of a semi-rigid board that derives its spring from a fulcrum mounted below the board and attached to the deck.
DPD – 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.
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. Dry Acid is safer to handle than muriatic acid.
Filter – A device that removes undissolved or suspended particles from water by re-circulating 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 Area – The total surface area of the filter medium that is exposed to the flow of water from the pump, expressed in square feet. Examples are: a 36 sq. ft. (also 36 ft) D.E. filter and a 100 sq. ft. (also 100 ft) cartridge filter.
Filtration Rate – The rate at which the water is traveling through the filter, expressed in U.S. gallons per minute (gpm) per square foot of filter area.
Flocculating AgentAlso flocculent – A chemical substance or compound that promotes the combination, agglomeration, aggregation or coagulation of suspended particles in the water.
Free Available 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.
GPM – An abbreviation for gallons per minute.
Green Hair – A condition caused by too much copper in the pool water. Green hair is not caused by chlorine. The copper may get into the water by the bad practice of placing trichlor tabs in the skimmer. This acidic product will cause low-pH water, which in turn will dissolve metals in the equipment. The dissolved metal )usually copper) then stains hair, fingernails, and, eventually, pool walls. It can also be caused by keeping the pH too low or misusing acid.
Heat Exchanger – A device located inside the heater providing for the transfer of heat from the heat source to the water. This is usually a series of metallic tubes with fins located just above the flames.
Hydrochloric AcidAlso called muriatic acid – A very strong acid used in pools to lower the pH and total alkalinity. It can also be used for various cleaning needs. Used in “acid washing” a pool. Use extreme care in handling.
Hypochlorite – The name given to a family of chlorine-containing compounds, including calcium hypochlorite, sodium hypochlorite and lithium hypochlorite, which are used as disinfectants and sanitizers in pool and spa water.
Hypochlorous Acid – The most powerful disinfecting form of chlorine in water. Sometimes called the killing form of chlorine.
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. Does not remove swimmer waste.
Iron – Iron in water causes the water to be brown- or green-colored. Can be controlled by the addition of a sequestering agent or a chelating agent. Water can be tested with an iron test kit.
Isocyanurates – Also called stabilized chlorine – A family of chorine pool sanitizers that contain conditioner (cyanuric acid or isocyanuric acid) to protect the chlorine from the degrading UV rays in sunlight. The most common types are sodium dichlor and trichlor. The 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.
Light Niche – The area in a pool or spa that houses the underwater light.
Liner – Also called Vinyl Liner – The vinyl membrane that acts as the container to hold or contain the water.
Liquid Acid (31.45% hydrochloric acid) – Also called muriatic acid – It is used for lowering pH, total alkalinity and for various cleaning needs. It is also used for acid washing.
Liquid Chlorine – A sodium hypochlorite 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. Good for regular chlorination and superchlorination.
Manifold – The branch pipe arrangement that connects several input pipes into one chamber or one chamber into several output pipes. A filter manifold connects several input pipes from the filter septa back into one common pipe.
Micron – A unit of length equal to 1 millionth of a meter – it is .000394 of an inch. Microns are used to describe the pore size of filter media. Sand filters have openings of 25 to 30 microns; cartridge filters have openings of 8 to 10 microns; and D.E. (diatomaceous earth) filters have openings of 1 to 5 microns. Humans, without magnification, can see objects 35 microns or larger. A granule of table salt is between 90 and 110 microns.
Mineral – Any substance that is neither animal nor vegetable. It is any class of substances occurring in nature, usually comprising of inorganic substances, such as quartz or feldspar, of definite chemical composition and definite crystal structure. It sometimes includes rocks formed by these substances. Ground water dissolves these rock substances, and the dissolved minerals are present in tap water. Depending on the kinds of rocks the water comes in contact with, the minerals dissolved in the water may be just a few or they may be many. Water hardness is mostly comprised of these minerals.
Multiport ValveAlso called a rotary-type backwash valve – This valve replaces as many as 6 regular gate valves. Water from the pump can be diverted for various functions by merely turning the valve handle. The water may be sent to waste, used for backwashing, bypassing the filter for maximum circulation, for normal filtration, filtering to waste (rinse), or the valve may be closed to not pass water. The pump must be off before changing a valve setting.
Muriatic Acid – (31.45% 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.
Organic WasteAlso called swimmer or bather waste – All of the soap, deodorant, suntan lotion, lipstick, makeup, cologne, body oils, sweat, spit, urine, etc., brought into the water. They also form chloramines, which are foul-smelling and body irritants. Requires large amounts of chlorine or non-chlorine chock to destroy.
OTO – Abbreviation for othotolidine. A chemical reagent used to test the total chlorine level in pool and spa water. It does not measure free available chlorine. See DPD.
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.”
Ozonator – Electrical devices which produce ozone from air or oxygen used for oxidation of water contaminants.
pH – A term used to indicate the level of acidity or alkalinity of pool water. Too low of pH causes etched plaster, metal corrosion and eye irritation. Too high of pH causes scale formation, poor chlorine efficiency and eye irritation. The ideal range for pH in swimming pools is 7.2 to 7.8.
pH of Saturation – Describes the ideal pH needed to achieve water balance in relation to the other factors on the Langelier Saturation index such as: alkalinity level, calcium hardness level, temperature etc.
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.
PPM – An abbreviation for parts per million in a weight-to-weight expression. It means 1 part in 1 million parts, such as 1 lb. of chlorine in 1 million lbs. of water. Many of the common pool water tests, as well as acceptable ranges, are stated as ppm. For example, free available chlorine should be kept between 1.0 and 3.0 ppm; total alkalinity should be between 80 and 120 ppm; and water hardness should be between 200 and 400 ppm.
Reagents – The chemical agents, dyes, indicators or titrants used in testing various aspects of water quality.
Sand – This usually refers to the filter medium used by a sand filter. The grade most often specified by filter manufacturers is grade No. 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.
Scale – The precipitate 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 grey, white or dark streaks on the plaster, fiberglass or vinyl. It may also appear as a hard crust around the tile.
Sequestering AgentAlso 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.
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. The weir also prevents debris from floating back into the pool when the pump shuts off.
Soda Ash – (sodium carbonate) – A chemical used to raise the pH and total alkalinity in pool and spa water.
Sodium Bicarbonate – (baking soda or bicarb) – A chemical used to raise the total alkalinity in pool and spa water with only a slight affect on the pH.
Sodium Bromide – A salt of bromine. It is used to establish a provide “bank” in pool and spa water prior to beginning the use of bromine tablets.
Sodium Carbonate – (soda ash) – A chemical used to raise the pH and total alkalinity in pool and spa water.
Stain – A discoloration or a colored deposit on the walls or bottom of a swimming pool or spa. Most often, stains are metals, such as iron, copper and manganese. They may appear as green, gray, brown or black. They may even discolor the water. Sometimes a sequestering agent or chelating agent will remove them. If not, usually an acid wash is necessary to remove them from the walls and bottom. The metals get in the water because the pH was too low or someone has added a low-pH chemical directly into the circulation system. The low-pH chemical dissolves a small amount of metal from the equipment. Then under certain conditions, the metals begin to come out of solution and deposit or stain the walls and bottom. Stains are sometimes confused with scale, which is a deposit of calcium or magnesium on the walls, bottom or in the equipment.
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.
Total Chlorine – The total amount of chlorine in the water. It includes both free available and combined chlorine.
Trichlor – A slow-dissolving, tableted or granular, stabilized organic chlorine compound providing 90% 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.
Water ClarifierAlso called coagulant or flocculant – 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.
Winterizing – The procedure for preparing the pool or spa for freezing weather. It includes chemical and physical treatment, such as draining, anti-freeze, drain plugs, etc., to protect the equipment, pool or spa.