ACID: A chemical substance containing hydrogen with the ability to neutralize alkaline materials. Acid is used to lower the pH or total alkalinity of swimming pool water. Most common are hydrochloric acid (muriatic) and dry acid (sodium bisulfate).
ACID DEMAND: The amount of acid required to bring high pH or total alkalinity down to their proper levels. Determined by an acid demand test.
ACID DEMAND TEST: A reagent test usually used in conjunction with a pH test to determine the amount of acid needed to lower pH or total alkalinity.
ACID RAIN: Precipitation having a low pH value caused by air polluted with sulfur dioxide, carbon dioxide or nitrous oxide.
AIR BLEEDER ASSEMBLY: See Air-Relief Valve
AIR-RELIEF VALVE: A manually operated valve located on the top of a filter tank for relieving the pressure inside the filter or for removing the air trapped inside the filter (bleeding the filter). Sometimes called a Pressure-Relief Valve.
ALGAE: Microscopic plant-like organisms that contain chlorophyll. Algae are nourished by carbon dioxide (CO2) and use sunlight to carry out photosynthesis. They find their way into the pool by rain or wind and grow in colonies, resulting in algae blooms. Algae do not cause disease, but provide an ideal substrate for bacteria to thrive in. There are over 21,000 known species of algae. The most common pool types are black algae, blue-green algae, green algae and mustard algae. Pink algae or red algae-like organisms can be found, but are in fact bacteria. Maintaining proper sanitizer levels, shock treatments and superchlorination will help to prevent or destroy algae.
ALGAECIDE: Meaning to kill algae. Algaecides perform best as a backup to a routine sanitation program. They also help to kill airborne spores as they blow into the pool. A variety of algae treatment products are available including copper and silver compounds, quat compounds, chlorine enhancers and herbicides. Algaecides are often formulated for a specific type of algae (green algae, mustard algae, black algae) with black algae being the hardest to treat.
ALGAESTAT: An algaecide kills algae, while an algaestat retards and prevents its development and growth.
ALGEA: See Algae
ALGICIDE: See Algaecide
ALKALI: Also called a Base. An alkali is the opposite of acid and is used to increase the pH or total alkalinity of swimming pool water. Most common are sodium carbonate or sodium hydroxide to increase pH, and sodium bicarbonate to increase total alkalinity.
ALKALINITY: Also called Total Alkalinity. A measure of the pH-buffering capacity of water or the water's resistance to change in pH. It is composed of the hydroxides, carbonates and bicarbonates in the water. When we measure the total alkalinity, we usually only measure the carbonate alkalinity level.
ALUMINUM SULFATE: Also known as Alum. This product is used as a flocculent, which attracts suspended particles in the water to each other. Alum sinks everything to the bottom, which can then be vacuumed to waste. A small amount of alum can also be used as a sand filter additive.
AMMONIA: (NH3) It is a nitrogen-containing compound introduced into the water by swimmers as waste (perspiration or urine) or by other means. It quickly combines with chlorine to form bad-smelling chloramines, which are harmful to our health.
ANTI-FOAM: A chemical added to the water to reduce the foam. These products do not remove the source of the foaming. Shocking and superchlorination may help prevent foaming. Careful use of cheaper algaecides/ algaestats can prevent foaming.
AUTOMATIC POOL CLEANER: A pool maintenance system that will brush or vacuum dirt and debris from the interior of the pool automatically. Some cleaners work on low-voltage electricity, others on the pump's suction line. The pool cleaner may be programmable, automatic or may move randomly around the pool. Some cleaners can climb the walls of the pool, while others only clean the floor.
AVAILABLE CHLORINE CONTENT: A term used to compare the amount of oxidizing power that chorine-containing products have when compared to gas chlorine (Cl2). It permits easy comparison of relative values of chlorine compounds.
AVAILABLE CHLORINE: The amount of free chlorine that is available to sanitize or disinfect the water. It is also called Residual Chlorine and Free Available Chlorine.

BACKFLOW: The backpressure of water in a pipe in the opposite direction to normal flow.
BACKWASH: Thoroughly cleaning a sand or D.E. filter by reversing the flow of water through it so that the dirt and rinse water go to waste.
BACTERIA: Unicellular microorganisms of various forms. Some are pathogens, which can cause infectious diseases. Bacteria are controlled by chlorine, bromine or other sanitizers or disinfectants.
BACTERICIDE: Meaning to kill bacteria. It is a chemical (e.g. chlorine) or an element (e.g. silver) that kills bacteria.
BAKING SODA: Chemically, Sodium Bicarbonate. It is white powder used to raise the total alkalinity of pool water without having much affect on pH. It will only increase pH up to 8.5, regardless of the quantity used. Care should be taken, however, to avoid adding large quantities at one time.
BALANCED WATER: Balanced water is the result when all of your chemical parameters are within the tolerance limits. The most important parameters of water balance are pH, Total Alkalinity, Calcium Hardness and Temperature, as measured using the Langelier Saturation Index.
BASE: Chemicals of alkaline nature, which will counteract the pH of an acid. Common bases used around the pool include Soda Ash, Sodium Bicarbonate and Sodium Carbonate. A base is the opposite of an acid. See Alkali
BASE DEMAND: A titration test used to determine the amount of a base (alkali) required to increase the pH to the correct level.
BCDMH: Chemically, "bromochlorodimethylhydantoin", it is a bromine sanitizer. When BCDMH dissolves in water it produces Hypobromous Acid and Hypochlorous Acid.
BICARB: See Sodium Bicarbonate.
BLEACH: This term usually refers to liquid chlorine. It is the same chemical used in the home, but pool chlorine (sodium hypochlorite) has 10% - 15% available chlorine while laundry bleach only has about 5% available chlorine.
BLEACHING OUT: At above 10ppm free available chlorine in a pool, a DPD test kit often indicates zero chlorine because the reagent is being destroyed. If you observe an initial pink color, which then rapidly fades, you probably have far too much residual chlorine in the water.
BIGUANIDES: The name for a certain class of sanitizers using the polymer PHMB, the only non-halogen sanitizer available for pool use. Soft Swim and Baquacil are manufacturers of this sanitizer. Biguanides are NOT compatible with pool chlorinators.
BLUE FINGERNAILS: A condition caused by too much free copper in the pool water. Can result from cheaper copper-based algaecides, overuse of these algaecides or corrosive water. See also Green Hair.
BOOSTER PUMP: In addition to the filter pump, a booster pump may be necessary to power some automatic pool cleaners.
BREAKPOINT CHLORINATION: When you shock treat your pool, the goal is to reach a high enough level of free chlorine to break apart all molecular bonds; specifically the combined chlorine molecules, ammonia or nitrogen compounds and to completely oxidize all organic matter. Adding enough chlorine to achieve this is breakpoint chlorination. Chlorine added after that point will be free available chlorine.
BROMAMINES: By-products formed when bromine reacts with swimmer waste (perspiration or urine), ammonia or nitrogen. Unlike chloramines, which are strong smelling and have very low sanitizing properties, bromamines are active disinfectants and do not smell, although high levels are harmful to your health.
BROMIDE: A common term for a bromide salt, which when added to water becomes hypobromous acid, the active form of bromine. It is used as a disinfectant in swimming pools.
BROMINATOR: A mechanical or electrical device for dispensing bromine at a controlled rate. It is most commonly a canister or floater filled with bromine tablets.
BROMINE: A member of the halogen family commonly used as a sanitizer or disinfectant to destroy bacteria and algae in swimming pools. It is resistant to heat and rapid pH fluctuations. Available as a tablet or as sodium bromide, a granular salt.
BUFFER: A chemical, which results in resistance to changes in pH. A base such as Sodium Bicarbonate, when added to your pool will increase total alkalinity. This in turn increases the buffering capacity of the pool; i.e. your pool's resistance to pH change.
BUFFERING CAPACITY: The ability of the pool to resist changes in pH. The buffering capacity is determined by the total alkalinity. If your pH bounces, or resumes previous levels soon after adjustment, the buffering capacity is too low. If your pH rises rapidly, even after the addition of large amounts of acid, the buffering capacity is too high. If the pool has an unstable pH, the total alkalinity should be tested and adjusted.
BYPASS: An arrangement of pipes, gates and valves by which the flow of water may be passed around the filter rather than through it, and usually refers to circulating the water without filtration.

CALCIUM CARBONATE: Crystalline compounds formed on swimming pool surfaces when the calcium hardness, pH or total alkalinity levels are too high. Once formed, the crystals adhere to the plumbing and pool surfaces. These crystals are also known as scale.
CALCIUM CHLORIDE: A soluble white salt used to raise the calcium hardness or total hardness level of pool water.
CALCIUM HARDNESS: The calcium content of the water. If the calcium hardness level is too low, the water may be corrosive. If the calcium hardness level is too high, the water may have a tendency to form scale.
CALCIUM HYPOCHLORITE: A compound of chlorine and calcium used as a disinfectant, sanitizer, bactericide, algaecide and oxidizer in swimming pool water. It is available as a white granular powder, which usually contains 65% - 70% available chlorine and has a pH of 11.8. It is also used as a disinfectant in drinking water.
CARBON DIOXIDE: A gas, which when present in the water, provides necessary nutrients for the algae to photosynthesize and reproduce in the presence of sunlight. Also used to lower pH in large pools.
CARTRIDGE: A disposable porous element made of paper or polyester, which is used as the filter medium in cartridge filters.
CARTRIDGE FILTER: A 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 in one direction only. Also called a one-way valve or a non-return valve.
CHELATOR: A chelating agent is a water soluble molecule that can bond tightly with metal ions, keeping them from coming out of suspension and depositing their stains and scale onto pool surfaces and equipment. Similar to sequestering agents.
CHELATED COPPER: Copper algaecides that contain a special ingredient to prevent the copper from staining the pool surfaces or producing colored water.
CHEMICAL FEEDER: A device that dispenses chemicals into the pool water at a predetermined rate. Some provide chlorine or bromine while others add pH-adjusting chemicals.
CHLORAMINES: Undesirable smelly compounds formed when insufficient levels of free available chlorine react with ammonia and other nitrogen containing compounds (swimmer waste, sweat, urine, ...). Chloramines are a threat to human health and are very poor sanitizers. Chloramines can be destroyed by shock treatment or superchlorination.
CHLORINATOR: A mechanical or electrical device for adding chlorine to a pool at a controlled rate. Most often a floater filled with tablets of chlorine or an in-line feeder.
CHLORINE: A member of the halogen family of sanitizers. Its use in swimming pools is in the form of a gas, as a liquid, in granular or tablet forms. When added to water it acts as an oxidizer, sanitizer, disinfectant and biocidal agent.
CHLORINE, combined: The measure of chlorine, which has attached itself to other molecules or organisms, typically ammonia or nitrogen, compounds. Most of these compounds are present as unwanted chloramines.
CHLORINE, free available: Free available chlorine is active chlorine and is not combined with any other molecule. A portion of the free available chlorine is present as hypochlorous acid, which reacts to destroy organic material in the pool water.
CHLORINE, total: The sum of combined and free available chlorine levels. With a DPD test kit, DPD1 determines free available chlorine and DPD3 shows total chlorine. The difference, if any, is the level of combined chlorine.
CHLORINE DEMAND: The amount of chlorine necessary to oxidize all organic matter (bacteria, algae, chloramines, ammonia and nitrogen compounds, . . .) in the pool water.
CHLORINE ENHANCER: A chemical compound used in conjunction with chlorine, that makes the chlorine perform better as an algaecide.
CHLORINE GENERATOR: An electrical device that generates chlorine from a salt solution. The salt solution may be in a separate tank or may be in the pool itself.
CHLORINE LOCK: If the level of cyanuric acid (stabilizer) in the water is much over 80ppm, the chlorine becomes trapped and is unable to oxidize effectively. Despite being able to measure normal chlorine levels, the Redox potential is very low, indicating a lack of oxidizer. The only way to fix this is to drain some of the water and refill the pool. Care should be taken when using stabilized chlorine products (dichlor or trichlor) to avoid the level of cyanuric acid increasing too much.
CHLORINE NEUTRALISER: A chemical used to deactivate or destroy chlorine. It is used in better test kits to prevent the bleaching effect of the chlorine and consequently to increase the accuracy of the tests.
CHLORINE RESIDUAL: Also called Free Available Chlorine. The amount of chlorine left in the pool water after the chlorine demand has been satisfied.
CLARIFIER: Also called a coagulant or flocculent. A chemical compound used to coagulate, clump or precipitate suspended microparticles so they can be removed by vacuuming or filtration. There are two main types; inorganic salts of aluminum (alum), or organic polyelectrolytes.
CLARITY: The degree or measure of the transparency of water.
CLINOPTILOLITE: The zeolite that is used as an alternative to quartz as the filter medium in sand filters.
COAGULANT: An organic polyelectrolyte that helps the filter by clumping minute particles together so they can be trapped by the filter.
COMBINED CHLORINE: See Chlorine, combined.
COMPENSATION TANK: The tank into which the water from the gutters or skimmer gutters flows. The tank serves to ensure that the pool has enough water to overflow regardless of the number of swimmers and independent of evaporation and splash-out losses.
CONDITIONER: Chemically known as cyanuric acid and also called stabilizer. It protects chlorine in the water against the effects of the sun's UV rays.
CONTAMINANTS: The general name for any microparticle or organism, which reduces water clarity, quality or presents health hazards. Filtering, oxidizing and sanitizing are necessary to destroy the contaminants.
COPPER: An effective algaestat and algaecide and is one of nature's natural elements. It may also be used in the equipment and plumbing in swimming pools. High levels of copper may stain hair, fingernails or pool surfaces and can also result in green, brown or blue water.
COPPER ALGAECIDE: A chemical compound that contains the element copper. Most copper algaecides contain ingredients that prevent the copper from staining but do not affect copper's ability to kill algae. These are known as chelated copper algaecides.
COPPER SULFATE: Copper sulfate was one of the original copper algaecides. It is similar to aluminum sulfate in that it provides a flocculent function in water. It can be used in ponds but may harm some aquatic creatures in high concentrations. The amount of copper required to be effective would stain swimming pools.
CORROSION: The effects of an acidic pool environment; one in which the pH and/or alkalinity are very low. Corrosion in the form of etching, pitting or erosion of pool equipment and surfaces is the result. May also be caused by misuse of acid or by soft water.
COVER, hard-top: A cover used on pools that rests on the edge of the pool deck and does not come into contact with the water.
COVER, solar: A floating cover that increases the water temperature by absorption and transmission of solar radiation and reduces evaporation and pollution from the environment.
COVER, winter: A cover that is secured around the edges of a pool when the pool is closed for the season.
CYANURIC ACID: Also called conditioner and stabilizer. A granular chemical added to the pool water, which provides a shield to chlorine for protection from the sun's UV radiation. It is also found in dichlor/ trichlor products.

D.E. FILTER: See Diatomaceous Earth Filter
DEFOAMER: Also called anti-foam. A chemical added to the water to destroy the foam. These products do not remove the source of the foaming. Shocking and superchlorination may help prevent foaming. Controlled use of certain of the cheaper algaecides can prevent their resulting in foaming.
DIATOMACEOUS EARTH: Also called D.E. A white powder composed of fossilized skeletons of unicellular 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 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 deposits the D.E. on a grid. The D.E. becomes the filter medium.
DICHLOR: The common name for Sodium Dichloro Isocyanuric Acid. A quick dissolving chlorine compound made up of chlorine and cyanuric acid (stabilizer) and has a pH of 6.9. Shock treatment with dichlor is not recommended as it may result in over stabilization and chlorine lock. If dichlor is used, a monthly check of the cyanuric acid level is recommended, to prevent over stabilization and chlorine lock.
DISINFECT: To kill all pathogenic (disease-causing) organisms.
DISINFECTANT: Chemicals, elements or processes, which destroy vegetative forms of microorganisms and other contaminants. Examples are chlorine, bromine, ionizers, ozonators and copper & silver algaecides.
DISSOLVED SOLIDS: See Total Dissolved Solids
DPD: Chemically, NN Diethyl-p-Phenylene Diamine Sulfate. An indicator reagent used to measure free available chlorine (DPD1) and total chlorine (DPD3), bromine, ozone and other oxidizers in water. Far superior to OTO.
DRAIN: A plumbing fitting installed on the suction side of the pump in pools. Also called the main drain, it is located in the deepest part of the pool. Main drains are connected to the pump for circulation, filtration and emptying of the pool.
DRY ACID: Chemically, sodium bisulfate. A dry white crystal that produces acid when added to water. It is used to lower pH and total alkalinity and is safer to handle than liquid acid (hydrochloric acid/ muriatic acid).

EPA: Abbreviation for the U.S. Environmental Protection Agency.
EFFICACY: The power to produce an effect. Chlorine's efficacy is affected by many factors, including the sun, temperature, water balance and the water's chlorine demand.
ENZYMES: Used in commercial swimming pool formulations to break down and destroy oils in the swimming pool.

FIBERGLASS: Fine threads of glass, which are available in the form of a rope or a mat. When polyester resins, catalysts and hardeners are applied to fiberglass, it can be formed or molded into pools, water tanks, boats and many other items.
FILL WATER: The water used in filling or topping up the swimming pool.
FILTER: A device that removes undissolved or suspended particles from water by the flow of the water through a porous substance (a filter medium or element). The three main types of filters used in pools are sand filters, cartridge filters and D.E. (diatomaceous earth) filters.
FILTER AID: A chemical compound added to the water, filter or skimmer that allows the existing filter to become more efficient. They are generally flocculants, coagulants and 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 meters.
FILTER CARTRIDGE: A disposable porous element made of paper or polyester and is used as the filter medium in cartridge-type filters.
FILTER CYCLE: The amount of time the filter has water flowing through it each day, expressed in hours.
FILTER ELEMENT: A device inside the filter, which is designed to trap suspended solids as water flows through it from the pool.
FILTER MEDIUM: The material used in the filter to trap suspended dirt particles as the water flows through it. It is the polyester or paper in a cartridge filter element, the sand in a sand filter and the diatomaceous earth in a D.E. filter.
FILTER POWDER: A common name for diatomaceous earth (D.E.), the filter medium in a diatomaceous earth filter.
FILTER ROCK: Graded, rounded rock and/or gravel, which is used to support the sand in sand filters.
FILTER SAND: Sand made up of hard and sharp silica or quartz (or similar), which have been graded for size and uniformity, and is used as the filter medium in sand filters. Nowadays it can also refer to clinoptilolite, the zeolite that is used as an alternative to quartz as the filter medium in sand filters.
FILTRATION RATE: The speed at which the water is traveling through the filter. Consult your owner's filter manual.
FLOC: See Flocculation.
FLOCCULANT: Also called a Flocculating Agent. Virtually the same as a coagulant, it is a chemical substance (such as alum) that is used to clump suspended particles or algae into a heavy mass, which can be caught by the filter or sinks to the bottom of the pool for vacuuming.
FLOCCULATION: The combination, clumping or coagulation of suspended particles so that they form small clumps or "lumps" (called floc).
FLOW RATE: The quantity of water flowing past a specific point in a specified time
FOAM: A froth of bubbles on the surface of the water. Usually comes from overuse of algaecide but may also be caused by soaps, oils or other contaminants carried into the water by swimmers. Enzymes may be used for foam control.

FREE AVAILABLE CHLORINE: The amount of free chlorine in the pool water that is available to oxidize, sanitize or disinfect the water. The level can be measured using a DPD1 test kit. It is also called residual chlorine or available chlorine.

GREEN HAIR: A condition caused by too much copper in the pool water or very high levels of chlorine.
GUNITE: A mixture of cement and sand which is sprayed onto the iron reinforced walls and floor of a hole to build a pool. The gunite surfaces are generally plastered.
GUTTER: Also called a Skimmer Gutter. An overflow channel at the edge of the pool through which floating debris, oil and other things flow and empty into the balance tank. Pools with gutters generally do not have skimmers.

HALOGENS: The chemical elements in Group VIIB of the Periodic Table of Elements: fluorine, chlorine, bromine and iodine. Only chlorine and bromine are used as oxidizers, disinfectants and sanitizers in swimming pools.
HAND SKIMMER: A net attached to a frame, which is then attached to a pole and is used to remove large floating pollutants such as leaves and insects from the water's surface.
HARD WATER: Water that is high in calcium, magnesium or other salts, which makes it difficult for soap to lather. Hard water also has a tendency to form scale.
HARDNESS, calcium: The amount of calcium dissolved in the water. It is usually measured as calcium carbonate.
HARDNESS, total: The amount of calcium, magnesium and other salts dissolved in the water.
HERBICIDE: A chemical compound used to kill or control plant or algae growth.
HYDROCHLORIC ACID: Also called muriatic acid. A very strong acid used in pools to lower the pH or total alkalinity. It can also be used for cleaning an empty pool (acid washing).
HYDROGEN: The lightest chemical element. It is a component of water and a product of many chemical reactions. pH is a measure of positive Hydrogen ions in water.
HYDROGEN PEROXIDE: An unstable, colorless liquid, which is used as an antiseptic in the home. It can be used as an oxidizing agent in pools. It is NOT compatible with pool chlorinators.
HYPOBROMOUS ACID: The active form of bromine in water.
HYPOCHLORITE: The name given to a family of chlorine compounds including: calcium hypochlorite, sodium hypochlorite and lithium hypochlorite. They are used as oxidizers, disinfectants and sanitizers in pool water.
HYPOCHLOROUS ACID: The active form of chlorine in water.

IMPELLER: The rotating part of a pump that is responsible for the movement of water through the pump.
INLET: A fitting in the pool on the water return line. Water is pumped back into the pool through the inlet after filtration.
IONISER: A water sanitizer that uses electricity to generate metal ions, usually copper and silver. It works by passing a current through a set of electrodes. The copper is an algaecide and algaestat, while the silver is a bactericide. Ionizers can significantly reduce chlorine consumption. If the ion levels get too high, problems with staining or discoloration of the water occur.
IRON: Iron is a natural element that can cause the water to become clear brown or green in color. It can also result in staining of the pool surfaces. Iron can be controlled by the addition of a suitable sequestering or chelating agent.
ISOCYANURATES: Also called stabilized chlorine. A group of chlorine pool sanitizers that contain stabilizer (cyanuric acid or isocyanuric acid) to protect the chlorine from the UV rays of the sun. The most common types are dichlor and trichlor. The granular form is dichlor, while the tablet or stick form is trichlor (usually used in a chlorine feeder). Stabilized chlorine should be used with care, to avoid problems such as chlorine lock that may be caused by over stabilization.

L.S.I.: See Langelier Saturation Index
LANGELIER SATURATION INDEX: Also called Langelier Index or Saturation Index. This index can be used to determine water balance according to the levels of pH, Total Alkalinity, Calcium Hardness and water Temperature. When all the parameters are in balance, the water will neither be corrosive or scaling.
LEAF NET: Also called a Hand Skimmer. A net attached to a frame, which is then attached to a pole and is used to remove large floating pollutants such as leaves and insects from the water's surface.
LINER: Also called a vinyl liner. The vinyl membrane that acts as the container to hold the water in one type of pool construction.
LIQUID ACID: Also called hydrochloric acid or muriatic acid. It is used for lowering pH, total alkalinity and for acid washing.
LIQUID CHLORINE: Chemically, sodium hypochlorite. It usually has 10% to 15% available chlorine and has a pH of 13. It is generally cheap, but difficult and dangerous to handle. It also loses its potency rapidly and is usually only used in large commercial pools.
LITHIUM HYPOCHLORITE: A dry granular chlorine compound with 35% available chlorine and has a pH of 10.7 . It dissolves quickly and can be used to superchlorinate vinyl-liner pools, painted pools and fiberglass pools.

MAGNESIUM HARDNESS: A measure of the amount of magnesium dissolved in the water. It is part of total hardness.
MAIN DRAIN: This usually refers to the drain that is located in the deepest part of the pool.
MAKE-UP WATER: Also called top up or refill water. It is the water used to replace water lost to evaporation, splash-out, leaks and backwashing.
MARBELITE: Also referred to as Plaster. It is a mixture of white cement and white marble dust used as an interior finish over the gunite or shotcrete of a pool. It can be given a color or it may be left white.
MARCITE: See Marbelite
MICRON: A unit of length equal to 1 millionth of a meter. 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 16 microns; and D.E. (diatomaceous earth) filters have openings of 1 to 5 microns. Zeolite used in sand filters has openings of 3 to 6 microns. A grain of salt is between 90 and 110 microns.
MICROORGANISM: An extremely small, living breathing creature. The purpose of disinfectants, sanitizers or oxidizers is to destroy these creatures in the pool water.
MINERAL: Substances such as Calcium, Manganese, Magnesium, Nickel, Copper, Silver, Zinc, Iron, Cobalt or Aluminum. Their presence in high non-chelated concentrations can lead to stains or scale formation. The measure of water hardness is dependent on these minerals.
MULTIPORT VALVE: Also called a 6-way or 6-port valve. Water from the pump can be diverted for various functions by turning the valve handle. The water may: (1) Be sent to waste, (2) Be used for backwashing, (3) Bypass the filter for maximum circulation, (4) Filter normally, (5) Be used to rinse the filter, or (6) The valve may have all its ports closed. The pump must be off before changing a valve setting.
MURIATIC ACID: Also called liquid acid or hydrochloric acid. A very strong acid used in pools to lower the pH and total alkalinity. It can also be used for cleaning an empty pool (acid washing).

NEUTRALISER: A chemical used to deactivate or destroy chlorine or bromine. It is used in better test kits in order to increase the accuracy of the pool water tests.
NITROGEN: A gas that causes algae to bloom and disables chlorine. It is introduced into the water by rain and by swimmers. Maintaining proper chlorine levels will prevent nitrogen from becoming a problem. Superchlorination can destroy nitrogen and nitrogenous compounds.
NON-CHLORINE SHOCK: A granular form of potassium peroxymonosulfate (potassium monopersulfate, potassium permonosulfate), used to oxidize materials such as microorganisms, contaminants (ammonia, nitrogen, swimmer waste, ...) or chloramines.

ORGANIC: Refers to chemical compounds containing carbon atoms bonded together with other elements. The main groups of organic substances found in water are proteins, carbohydrates, fats and oils.
ORGANIC WASTE: Also called swimmer or bather waste. Refers to the soap, deodorant, suntan lotion, body oils, sweat, spit, urine . . . , that is introduced into the water by swimmers, as well as the leaves, dust and insects that end up in the pool. The organic waste may form undesirable chloramines, which require large amounts of chlorine or non-chlorine shock to be destroyed.
ORP: The abbreviation for Oxidation-Reduction Potential. It is a measurement of the oxidizer’s (e.g. chlorine) ability to oxidize contaminants versus the contaminants' (e.g. algae) ability to reduce the oxidizer. It is an indication of the level of free available oxidizer in the water. ORP is generally used with automated dosage systems and can give a fair idea of the sanitation of the water. It is not a measure of the total or available chlorine. Sometimes called Redox Potential.
OTO: The abbreviation for Ortho Tolidine. A chemical reagent used to test the total chlorine level in water at normal temperatures. It can measure free available chlorine if the water is first cooled to 1°C. Its results depend on pH, time and concentration of chlorine. Due to its toxicity, the use of OTO is restricted or prohibited in many western countries.
OXIDATION: The burning up or destruction of organic waste and organic compounds in the pool water.
OXIDISER: Any compound that removes or destroys organic waste and organic compounds in the water.
OZONATOR: An electrical device that produces ozone that is introduced into the water as a sanitizer.
OZONE: A molecule containing three atoms of oxygen. It is known to be a very powerful sanitizer. Ozone producing equipment creates this molecule by UV radiation or corona discharge generators.

PATHOGEN: Also called a pathogenic organism. An organism that can cause illness, disease or death.
pH: A term used to indicate the level of acidity or alkalinity of water. A pH of 7.0 is neutral; below 7 is acidic; above 7 is alkaline or basic. pH is a logarithmic expression of the measure of positive Hydrogen ions in water. The ideal range for pH in swimming pools is 7.0 to 7.6. The pH of our tears is 7.2 to 7.4 .
PHENOL RED: A chemical reagent dye used to test pH. It can measure pH from 6.8 to 8.4 . The tablet form usually incorporates a chlorine neutralizer for more accurate results.
PHOTOMETER: An electrical instrument for testing pool water conditions, which measures the colors electronically rather than visually, giving more accurate results.
PLASTER: Also referred to as Marbelite. It is a mixture of white cement and white marble dust used as a finish over the gunite or shotcrete of a pool. It can be colored or it may be left white.
POLYMER: A large substance comprising of small repeating molecules. Many coagulants are made from organic polymers, as are algaecides and algaestats.
POTASSIUM PEROXYMONOSULFATE: See Non-chlorine Shock.
ppm: The abbreviation for parts per million. It is a method of assigning value to concentrations of chemicals in the water. Many of the common pool water tests, as well as acceptable ranges, are stated as ppm. 1ppm = 1 mg/L
PRECIPITATION: To precipitate is to come out of solution or to become insoluble as a result of a chemical reaction. Material forced out of solution will settle, stain, scale or remain suspended in the water.
PRESSURE GAUGE: A gauge with a dial indicating the pressure in a closed container such as a sand filter.
PUMP: A mechanical device, which causes water to flow under pressure for the purpose of filtration or circulation.
PUMP CAPACITY: The volume of water a pump is capable of moving during a specified period of time. Consult your pump owner's manual.
PUMP CURVE: Also called a Pump Performance Curve. It is a graph that shows a pump's water flow capacity at any given resistance.
PUMP STRAINER BASKET: A device placed on the suction side of the pump, which contains a removable strainer basket designed to trap large debris in the water flow without causing restriction. Sometimes called a Pump Leaf Trap.

QUATERNARY AMMONIUM COMPOUNDS: Also called Quats or QAC. A type of algaecide composed of ammonia compounds. They are also effective algaestats for certain types of algae.

RATE OF FLOW: The volume of water flowing past a point within a specified time.
REAGENTS: The chemical indicators used in testing various aspects of water quality.
REDOX POTENTIAL: The abbreviation for Reduction-Oxidation Potential. It is a measurement of the oxidizer’s (e.g. chlorine) ability to oxidize contaminants versus the contaminants' (e.g. algae) ability to reduce the oxidizer. It is an indication of the level of free available oxidizer in the water. ORP is generally used with automated dosage systems and can give a fair idea of the sanitation of the water. It is not a measure of the total or available chlorine. Sometimes called ORP.
RESIDUAL BROMINE: The amount of free available bromine remaining in the water after the bromine demand has been satisfied.

RESIDUAL CHLORINE: The amount of free available chlorine remaining in the water after the chlorine demand has been satisfied.

SAND: The filter medium used by a sand filter. It usually refers to quartz or silica, but may also refer to zeolites.
SAND FILTER: A filter using sand, or sand and gravel as the filter medium.
SANITISE: To kill all microorganisms, including bacteria and algae, and to remove unwanted contaminants.
SCALE: The precipitate that forms on surfaces in contact with water when the calcium hardness, pH or total alkalinity levels are too high. Scale may appear as grey, white or dark streaks on the plaster, fiberglass or vinyl. It may also appear as a hard crust at the waterline.
SCUM: The foreign matter, which floats to the surface of the water and forms a layer or a film. It can also refer to a residue deposited on the tiles or walls of the pool.
SEDIMENT: The solid material that precipitates out of the water and settles to the floor of the pool.
SEQUESTERING AGENT: Also called Chelating Agent. A chemical or compound that combines with dissolved metals or minerals in the water to prevent them from coming out of solution, thus coloring the water or causing stains.
SEQUESTRANT: A chemical, which holds metals in solution and helps prevent scaling. See Sequestering Agent.
SHOCK TREAT: Adding large amounts of an oxidizer such as chlorine, hydrogen peroxide or potassium peroxymonosulfate to the water to destroy ammonia and nitrogen compounds, chloramines and other contaminants.
SHOTCRETE: Similar to Gunite, but premixed.
SKIMMER: A device installed in the wall of a pool that is connected to the suction line of the pump. The suction pulls in water and floating contaminants.
SKIMMER BASKET: A removable basket or strainer placed in the skimmer, which is designed to trap large solids from the water before they get to the pump or filter.
SKIMMER GUTTER: Also called a Gutter. An overflow channel at the edge of the pool through which floating debris, oil and other things flow and empty into the compensation tank. Pools with gutters generally do not have skimmers.
SKIMMER NET: A net attached to a frame, which is then attached to a pole and is used to remove large floating pollutants such as leaves and insects from the water's surface.
SKIMMER WEIR: The small floating door on the side of the skimmer over which water flows on its way to the skimmer. The weir prevents debris from floating back into the pool when the pump is off.
SLURRY: Water containing a high concentration of suspended solids. D.E. is usually added to the filter as a slurry by mixing the D.E. in some water.
SODA ASH: Chemically, Sodium Carbonate. A base that is used to raise the pH of acidic (below pH 7.0) water.
SODIUM BICARBONATE: Also called Baking Soda or Bicarb. A base that is used to raise Total Alkalinity in pool water with only a slight effect on the pH. Sodium bicarbonate can only raise the pH of the water to 8.5, regardless of the amount used. Care should be taken, however, to avoid adding large quantities at one time.
SODIUM BISULFATE: Also called Dry Acid. A granular form of acid used to lower the pH or Total Alkalinity of pool water.
SODIUM BROMIDE: A salt of bromine, which is used to raise the bromine levels in a pool before using bromine tablets.
SODIUM CARBONATE: Also called Soda Ash. A base that is used to raise the pH of acidic (below pH 7.0) water.
SODIUM DICHLOR: A granular, stabilized organic chlorine compound providing 56% or 62% available chlorine that has a pH of 6.9. Used for regular chlorination. Should be used with caution for superchlorination as it can cause the stabilizer level to rise too high, resulting in chlorine lock.
SODIUM HYPOCHLORITE: Liquid chlorine for use in pools. It usually provides 10% to 15% available chlorine and has a pH of 13. It is generally cheap, but difficult and dangerous to handle. It also loses its potency rapidly and is usually only used in large commercial pools.
SODIUM MONOPERSULFATE: Active ingredient and chemical name of a non-chlorine shock treatment or non-chlorine oxidizer. See Non-Chlorine Shock.
SODIUM PERSULFATE: Active ingredient and chemical name of a non-chlorine shock treatment or non-chlorine oxidizer. See Non-Chlorine Shock.
SODIUM SULFITE: A chemical that can be used to neutralize chlorine or dechlorinate pool water.
SODIUM THIOSULFATE: A chemical that can be used to neutralize chlorine or dechlorinate pool water.
SOFT WATER: Water that has a low calcium and/or magnesium content. Soft water can result in the etching of the pool's surfaces, and should be increased with calcium chloride.
SOLAR COVER: A floating pool cover that increases the water temperature by absorption and transmission of solar radiation. It also reduces evaporation and pollution from the environment.
SOLAR HEATING SYSTEM: A system that consists of panels through which the pool water passes to increase its temperature by using the sun's heat.
STABILIZED CHLORINE: A family of organic chlorine compounds that contain stabilizer (cyanuric acid or iso-cyanuric acid) to protect the chlorine from the degrading UV rays in sunlight. Most common types are dichlor and trichlor. The granular form is dichlor and the tablet or stick form is trichlor.
STABILIZER: Also called Cyanuric Acid or Conditioner. A granular chemical added to the pool water, which provides a shield to chlorine for protection from UV radiation. Too much can result in chlorine lock.
STAIN: A discoloration or a colored deposit on the walls or bottom of a swimming pool. Stains are usually the result of metals such as iron, copper or manganese in the water. The stains may be green, gray, brown or black. They may discolor the water without affecting the clarity. Sometimes a sequestering agent, chelating agent or commercial stain-remover may remove them. If that doesn't work, the easiest way to remove the stains is to drain and acid wash the pool.
STAIN INHIBITOR: Also called a Sequestering or Chelating Agent. A chemical that will combine with dissolved metals in the water to prevent the metals from coming out of solution and so avoiding discoloration of the water or stains.
SUPERCHLORINATION: Adding 7 - 10 times the normal dose of chlorine to the water to destroy ammonia, nitrogen, chloramines and other contaminants.
SUSPENDED SOLIDS: Insoluble solid particles that either float on the surface or are in suspension in the water causing cloudiness. They may be removed by filtration, but if the particles are too small a flocculent or coagulant is necessary to enable the filter to trap them.

TDS: See Total Dissolved Solids
TEST KIT: A manual or electrical device used to measure specific chemical residuals, levels or demands in pool water. Kits usually contain reagents, vials, titrants and color comparators for the tests. The most common tests are: pH, free available chlorine, combined chlorine, total alkalinity, calcium hardness, cyanuric acid and metals.
TEST STRIPS: Small plastic strips with pads attached that have been impregnated with reagents to test pool water. The strips are dipped into the water and the resulting colors are compared to a color scale to determine the values.
TIME CLOCK: Also called a Timer. An electrical device that automatically turns the pump or pool cleaner on or off at predetermined intervals or times.
TITRATION: A method of testing for total alkalinity, calcium hardness and acid/base demand by adding a titrant, drop by drop, until a color change is observed.
TOTAL ALKALINITY: The total amount of alkaline materials present in the water, usually measured as carbonate alkalinity. It indicates the water's resistance to change in pH. Low total alkalinity causes pH bounce. High total alkalinity causes the pH to constantly rise.
TOTAL CHLORINE: The total amount of chlorine in the water. It is the sum of free available chlorine and combined chlorine.
TOTAL DISSOLVED SOLIDS: Also called TDS. A measure of everything that has ever dissolved in the water and all the matter that is in solution. The only way to lower TDS is to drain part of the water and replace it.
TRICHLOR: A slow dissolving tablet or granular stabilized organic chlorine compound, which provides 90% available chlorine and has a pH of 2.9. It must be dispensed using a floating feeder or an in-line chlorinator. Trichlor contains cyanuric acid that prevents the chlorine from being destroyed by the ultraviolet rays of the sun. When using trichlor, the cyanuric acid level needs to be checked regularly to avoid chlorine lock.
TURBIDITY: The cloudy condition of the water due to the presence of extremely fine particles in suspension that are able to pass through the filter. Adding a flocculent or coagulant will clump the particles together so they can be trapped in the filter.
TURNOVER: Also called Turnover Rate. The period of time, in hours, required by the pump to circulate the volume of water in the pool.  Consult your pump owner's manual for turnover rate.

ULTRAVIOLET LIGHT TREATMENT: Using UV wavelength radiation to destroy contaminants in water. UV light is also used to create ozone molecules for the same purpose.
UNDERWATER LIGHT: A light fixture designed to illuminate a pool from below the water's surface.

VACUUM: A device that uses suction to collect dirt from the bottom and sides of a pool. Most common is a vacuum head with wheels that attaches to a pole and is connected to the suction line. Some automatic pool cleaners fall into this category.
VINYL LINER: Also called a Liner. The vinyl membrane that acts as the container to hold the water in one type of pool construction.
VIRUS: A pathogen capable of causing disease.

WASTE GUTTER: The outer channel in a pool with 2 gutters. The inner channel (skimmer gutter) returns the water for filtration, while the outer one collects rain or wash water and diverts it to waste before it can enter the pool.
WATER CLARIFIER: See Coagulant/ Flocculent.
WEIR: Also called a Skimmer Weir. The small floating door on the side of the skimmer over which water flows on its way to the skimmer. The weir prevents debris from floating back into the pool when the pump is off.

ZEOLITE: An alternative to quartz or silica for use in sand filters. It is typically clinoptilolite, the specific zeolite suitable for pool water conditions. Zeolite can provide filtration down to 3 microns, is able to absorb heavy metals such as iron or manganese, and absorbs ammonia and nitrogen compounds. Zeolite can also absorb chloramines and is regenerated by washing in salt. Being less dense than quartz, 60% - 70% of the weight of quartz is used. Zeolite is also claimed to reduce backwashing by 50%.