POOL GLOSSARY 

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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 Demand: The amount of acid required to bring high pH and total alkalinity down to their proper levels. Determined by the 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 and total alkalinity levels.

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.

Acrylic: A thermoplastic sheet formed into a mold to make a spa or related equipment. It is first heated and then vacuumed onto the mold.

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 plant-like organisms that contain chlorophyll. Algae are nourished by carbon dioxide (CO2) and use sunlight to carry out photosynthesis. It is introduced by rain or wind and grows in colonies producing nuisance masses. Algae are not disease-causing, but can harbor bacteria, and it is slippery. There are 21,000 known species of algae. The most common pool types and black, blue-green, green and mustard (yellow or drawn). Pink or red-colored algae-like organisms exist but are bacteria and not algae. Maintaining proper sanitizer levels, shocking and superchlorination will help prevent its occurrence.

Algaecide: Also called algicide; a natural or synthetic chemical designed to kill, destroy or control algae.

Alkali: Also called base; a Class of compounds which will react with an acid to give a salt. Alkali is the opposite of acid.

Alkalinity: Also 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.

Alum: Any one of several aluminum compounds used in pools to form a gelatinous floc on sand filters or to coagulate and precipitate suspended particles in the water.

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.

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 and superchlorination may help prevent foaming.

Ascorbic Acid: A chemical compound used to remove iron stains from fiberglass and vinyl-liner pools.

Automatic Pool Cleaner: A pool maintenance system that will agitate or vacuum debris from the pool interior automatically.

Available Chlorine Content: A term used or an index used to compare the oxidizing power of chorine-containing products to gas chlorine. It permits easy comparison of chlorine compounds.

Available Chlorine: The amount of chlorine, both free and combined in the pool water that is available to sanitize or disinfect the water. Some- times called residual chlorine.

Backflow: The backing up of water through a pipe in the direction opposite to normal flow.

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.

Bacteria: Single-celled microorganisms of various forms, some of which are undesirable or potentially disease-causing. Bacteria are controlled by chlorine, bromine or other sanitizing and disinfecting agents.

Bacteridice: A chemical or element that kills, destroys or controls bacteria.

Baking Soda: Chemically called sodium bicarbonate. It is white powder used to raise the total alkalinity of pool or spa water without having much affect on pH.

Balanced Water: The correct ratio of mineral content and pH level that prevents the water from being corrosive or scale forming.

Ball Valve: A simple non-return valve consisting of a ball resting on a cylindrical seat within a liquid passageway.

Base: Also called basic; a class of compounds which will react with an acid to give a salt. Base is the opposite of an acid. See alkali.

Bleach: This term usually refers to liquid chlorine (sodium hypochlorite 12% available chlorine). It is the same chemical used in laundry bleach but pool chlorine is 12% available chlorine while laundry bleach is about 5 to 6%% available chlorine.

Blower: An electrical device that produces a continuous rush of air to create the optimal bubbling effect in a spa, hot tub or whirl- pool. It is usually plumbed in with the hydrotherapy jets or to a separate bubbler ring.

Blue Fingernails: A condition caused by too much copper in the pool water. Blue finernails are 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 will in turn 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.

Breakpoint Chlorination: The process of adding sufficient free available chlorine to completely oxidize all organic matter and ammonia or nitrogen compounds. 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.

Bromides: A common term for a bromide salt used to supply bromide ions to the water so they may be oxidized or changed into hypobromous acid, the killing form of bromine. Used as a disinfectant.

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

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.

BTU: Abbreviation for British Thermal Unit. The amount of heat necessary to raise 1 lb. of water 1 degree Fahrenheit.

Buffer: A substance or compound that stabilizes the pH value of a solution. It is also the water's resistance to change in pH.

Bypass: An arrangement of pipes, gates and valves by which the flow of water may be passed around a piece of equipment or diverted to another piece of equipment; a controlled diversion.

Calcium Hypochlorite: A compound of chorline and calcium used as a disinfectant, sani- tizer, 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.

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 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.

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

Cartridge: 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.

Centrifugal Pump: A pump consisting of an impeller fixed on a rotating shaft and enclosed in a casing or volute and having an inlet and a discharge connection. The rotating impeller creates pressure in the water by the velocity derived from the centrifugal force.

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.

Chelated Copper: Copper algaecides that contain a special ingredient to prevent the copper from staining the pool walls and bottom 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.

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.

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. Chloamines 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 Demand: The amount of chlorine necessary to oxidize all organic matter (bacteria, algae, chloamines, 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 Generator: An electrical device that generates chlorine from a salt solution in a tank or from salt added to the pool water. Also called a salt generator or salt chlorinator.

Chlorine Lock: This is a term that implies that an over-abundance of cyanuric acid (stablizer or conditioner) in the water would cause the chlorine to be all "locked up." This is not true.

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

Clarifier: Also called coagulant or flocculant; achemical compound used to gather (coagulate or agglomerate), or to precipitate suspended particles so they may be removed by vacuuming or filtration. The are two types; inorganic salts of aluminum (alum) or water- soluble organic polyelectrolytes.

Clarity: The degree of transparency of the water.

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: Chemically, conditioner is cyanuric acid. It slows down the degradation of chlorine in the water by sunlight. Minimum level is 10 ppm. Too much does not slow down chlorine activity or effectiveness.Conditioner does not protect bromine from sun- light.

Coping: The cap or top lip on the pool or spa wall that provides a finished edge around the pool or spa. It can be formed, cast in place or precast, or prefabricated 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: 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, improper water balance, or placing trichlor tablets in the skimmer can cause copper to be dissolved from the equipment or plumbing and deposit the precipitates on hair, finger- nails or pool walls. High levels of copper also cause green water. Copper is also used as an algaecide. Maximum level is about 0.2 ppm.

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.

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

Coupling: A plumbing fitting that is used to connect two pieces of pipe.

Cover, Hard-Top: 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, and for maintenance and thermal protection.

Cover, Solar: 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 wine-borne debris from entering the water.

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 Acid: Also called condition 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.

D. E. Filter: 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 takes the D.E. and deposits it on a grid. The D.E. then becomes the filter medium.

Decks: Those areas immediately adjacent to a pool, spa or hot tub that are specifically constructed or installed for use by bathers for sitting, standing or walking.

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 suds. Most often, the water must be drained and refilled to remove the soaps, oils and other causes of foaming. Shocking and super-chlorination may help prevent foaming.

Diatomaceous Earth: Also called D.E.; awhite 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.

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.

Diffuser: A porous plate, tube or other device through which air is forced and divided into minute bubbles for diffusion in the water. A diffuser can also be an overdrain on a sand filter. A difuser is also used on a closed- face impeller on a pump to concentrate water flow to the center of the impeller.

Disinfect: To kill al pathogenic (disease-causing) organisms.

Dissolved Solids: Also called TDS or total dissolved solids; a measure of the total amount of dissolved matter in water. Examples are calcium, magnesium, carbonates, becarbonates, solium, chlorides and metals. High levels can cause corrosion, colored water or salty taste. Maximum level is usually 2500 ppm for pools. Maximum level for spas is 1500 ppm over starting level.

Divertor Valve: A plumbing fitting used to change the direction or redirect the flow of water. Some diverter valves are used on pool/spa combinations to allow the use of the spa and then switch the flow back to the pool. A brand name diverter valve is called an Ortega valve, which is sometimes used to describe a diverter valve.

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.

Drain: This term usually refers to a plumbing fitting installed on the suction side of the pump in pools, spas and hot tubs. Sometimes called the main drain, it is located in the deepest part of the pool, spa or hot tub. It is not a drain, such as a drain on a kitchen sink. Main drains do not allow the to drain to waste but rather connect to the pump for circulation and filtration.

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

Effluent: The water that flows out of a pump, filter or heater, usually on its way back to the pool or spa.

Elbow: A plumbing fitting shaped at a 90 degree or a 45 degree angle usually made of metal, PVC or some other plastic.

Electrolosis: An electrochemical reaction causing a black stain normally found around metal fixtures or on the plaster. It is caused by two dissimilar metals being plumbed together or from an improper electrical grounding of pool equipment or lights. Electrolysis also means the decomposition of water and other inorganic compounds in aqueous solution by means of electricity. Chlorine generators use this principle to produce chlorine from salt in the water.

EPA: Abbreviation for the federal Environmental Protection Agency.

Escutcheon Plate: An ornamental shield, flange or border used around a pie, plumbing fitting, grab rail or light.

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

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

Filter Area: The toal 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 ft2) D.E. filter and a 100 sq.ft. (also 100 ft2) cartridge filter.

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

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 flows through it from the pool or spa.

Filter Medium: 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.

Filter Powder: A common name for diatomaceous earth (D.E.), used as the filter medium in a diatomaceous earth filter.

Filter Rock: Graded, rounded rock and/or gravel used to support the filter medium. Usually used with rapid-rate sand filters.

Filter Septum: That portion of the filter element consisting of cloth, wire screen or other porous material on which the filter medium or filter aid is deposited. The nylon grid on a D.E. filter is the septum.

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

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.

Fireman's Switch: A mechanical switch located inside the time clock, which opens a circuit and shuts off the heater 10 or 15 minutes prior to shutting off the water circulation pump, allowing the heater to cool down. This helps reduce lime buildup in the heat exchanger.

Floc: (See flocculation) 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).

Flow Rate: The quantity of water flowing past a designated point within a specified time, such as the number of gallons flowing past a point in 1 minute - abbreviated as gpm.

Foam: A froth of bubbles on the surface of the water. Usually comes from soap, oil, deodorant, hair spray, suntan oil, etc., that is shed into the water as swimmers enter.

Free Available Chorine: 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.

Gelcoat: A colored, polyester-resin material applied to the surface of a molded part. The gelcoat hardens to a smooth, durable form and becomes an integral part of the laminate. Fiberglass pools and spas have gelcoat finishes.

GPD: An abbreviation for gallons per day.

GPH: An abbreviation for gallons per hour.

GPM: An abbreviation for gallons per minute.

Grab Rail: Also called handrail; a tubular steel or plastic device that can be gripped by swimmers or bathers for the purpose of steadying themselves. Usually located near the steps in the pool.

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.

Ground-Fault Circuit-Interrupter: Also called a GFI; a device intended to protect people. It interrupts (de-energizes) the electrical circuit whenever it detects the presence of excess electrical current going to ground (usually 1/40th of a second and 5/1000th of an ampere).

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 the point of application. Plaster or pebble is usually applied over the gunite.

Gutter: An overflow trough at the edge of the pool through which floating debris, oil and other "lighter-than-waste" things flow. Pools with gutters usually do not have skimmers.

Halogens: The chemical elements either individually or collectively that constitute Group VIIB of the Periodic Table of Elements: fluorine, chlorine, bromine, iodine and astatine. Of these, only chlorine and bromine are used as disinfectants and sanitizers in pools and spas.

Hand Rail: A tubular steel or plastic device that can be gripped by swimmers or bathers for the purpose of steadying themselves. Usually located near the steps in the pool.

Hand Skimmer: Also called leaf skimmer; a screen attached to a frame which is then attached to a telepole used to remove large floating debris, such as leaves and bugs, from the water's surface.

Hardness: The amount of calcium and magnesium dissolved in the water."Water" or "total" hardness refers to the total magnesium and calcium dissolved in the water. Calcium hardness refers to just the calcium. Measured by a test kit and expressed as ppm. The proper range is 200 to 400 ppm.

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.

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

Herbicide: A chemical compound used to kill or control plant growth or algae. Simazine is a common pool herbicide.

Horsepower: The work done per unit of time. 1 horsepower equals 33,000 foot-pounds of work per minute or approximately 746 watts. Motors for pumps are rated in horsepower.

Hot Tub: A spa constructed of wood with the sides and bottom formed separately and joined together by hoops, bands or rods.

Hydrochloric Acid: Also 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.

Hydrogen: The lightest chemical element. A component of water, and a frequent product of many chemical reactions. pH is a measure of hydrogen in its ionic form in water.

Hydrogen Ion: The positively charged nucleus of hydrogen atom. The relative degree of acid or base of a solution (called pH) is a measure of hydrogen ions.

Hydrogen Peroxide: An unstable, colorless, heavy liquid used as a bleach in industry and as an antiseptic in households. It is used as an oxidizing agent in pools and spas. May also be used to de- chlorinate pool or spa water.

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.

Hypobromous Acid: The most powerful disinfecting form of bromine in water. Sometimes called the killing form of bromine.  

Hypochlorite: The name given to a family of chlorine containing compounds, including calcium hypochlorite, sodium hypochlorite and lithium hypochlorite, that 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.

Impeller: The rotating member of a pump. The part of the pump that moves the water.

Influent: The water entering the pump, the filter or other equipment of space. Water going into the pump is called in influent, while water leaving the pump is called the effluent.

Inlet: A fitting in the pool or spa on the water return line from the equipment that water returns to the pool.Usually the last thing on the return line

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-collored. 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 chlorine pool sanitizers that contain conditioner (cyanuric acid or isocyanuris 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 broadcasing into the pool or spa. Tablet or stick form is trichlot (which is usually used in a chlorine feeder - either the floating type or the in-line erosion type) used for regular chlorination only.

Jacuzzi: A brand name and registered trademark for a specific line of spas and whirlpools.

Ladder: A structure for climbing up or down; consists of two parallel sides joined by a series of crosspieces that serve as footrests.It is used for getting in and out of the pool. A double-access ladder straddles the pool wall of an above ground pool. An in-pool ladder is located in the pool only.

Leaf Bagger: A device that attaches to a telepole and a garden hose. Pressure from the garden hose creates a suction by which leaves and large debris are sucked into a large mesh bag.

Light Niche: The area in a pool or spa that house the underwater light.

Liner: Also called vinyl line; 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.

Lithium Hypochlorite: A dry, granular chlorinating compound with an available chlorine content of 35%. It is rapid-dissolving and can 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.

Main Drain: This term usually refers to a plumbing fitting installed on the suction side of the pump in pools, spas and hot tubs. Sometimes called the drain and is located in the deepest part of the pool, spa or hot tub. It is not a drain, such as a drain on a kitchen sink. Main drains do not allow the water to drain to waste but rather connect to the pump for circulation and filtration.

Make-Up Water: This is 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.

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.

Marcite: Originally a brand name for a white plaster finish coat from 1/8th to 1/2 inch thick applied over the gunite or shotcrete.

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 to 110 microns.

Mineral: Any substance that is neither animal or 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 Valve: Also 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.

Muratic 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.

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