Swimming Pool Terminology

A
Acid	A chemical compound which releases hydrogen ions into water, decreasing pH. Products containing muriatic acid or sodium bisulfate are used to adjust pH and total alkalinity in pool water. See pH
Acid Demand	The amount of acid needed to lower pH to the proper level for pool water.
Algae	Microscopic plants deposited in pool or spa water by wind, rain and dust. They thrive in sunlight and warm water, clogging pool equipment and causing slippery surfaces and green water. There are 21,000 known species of algae.
Algicide	A chemical added to pool water to kill algae infestations and prevent their recurrence.
Alkalinity	The amount of carbonate, bicarbonate and hydroxide compounds in pool water. See Total Alkalinity
Alum	Aluminum sulfate added to pool water causing suspended particles to sink so they can be filtered or backwashed out.
Ammonia	A nitrogen containing compound that combines with free chlorine to form chloramines. Chloramines have a strong chlorine odor and can cause skin and eye irritation.
Available Chlorine	The amount of total oxidizing power (ability to kill bacteria) a chlorine product contains. Also referred to as free chlorine in pool or spa water.
top B
Backwash	Reversing flow of water through the filter to clean the elements and filter medium.
Backwash Cycle	The time needed to backwash (clean) the filter and its components, using a reverse flow of water.
Bacteria	Single-celled microscopic organisms that can cause infections, disease and other bather irritation. Chlorine is use to kill bacteria in pool and spa water.
Balanced Water	Pool water that has a proper pH and the proper mineral content (total alkalinity, calcium hardness) to prevent corrosion and scaling.
Base	A chemical that neutralizes acids by releasing carbonate and/or hydroxide ions. Used in pools to raise the pH level. Also referred to as "alkaline".
Bather	Anyone using the pool, spa, hot tub or the surrounding deck.
Bather Load	The number of people in a pool or spa at a particular time or during a specific period of time.
Breakpoint	During chlorination, this is the point at which all combined chlorine is oxidized (removed) and only free chlorine remain in the water to kill bacteria.
Breakpoint Chlorination	Adding enough chlorine to pool water to oxidize all combined chlorine present.
Bromamines	Non-irritating bromine-ammonia compounds that have sanitizing capabilities similar to hypobromous acid (HOBr). See Chloramines
Bromide	Sodium and potassium bromide salts used as one component of a spa disinfectant or algicide. Bromide itself is not a disinfectant but can be activated to hypobromous acid with chlorine or potassium mono-persulfate.
Brominator	A device that dispenses bromine tablets into pool water in a controlled, gradual manner.
Bromine	A chemical used in various compound forms to sanitize pool and spa water. It forms hypobromus acid in water.
Buffer	Sodium Bicarbonate or other basic chemical added to pool water to prevent fluctuations in pH.
top C
Calcium Carbonate	Scale that forms from calcium compounds when the pool water is to alkaline, calcium hardness is too high or total alkalinity is too high. These hard deposits accumulate on pool surfaces and equipment.
Calcium Chloride	A soluble salt added to pool water to raise the calcium hardness level.
Calcium Hardness	The amount of dissolved calcium in pool water.
Cartridge	A porous, replaceable element in some filters. Depth type cartridges have a medium at least 3/4 inch (.18 cm) thick. Particulates are removed when they penetrate into the medium. Surface type cartridges have a medium less than 3/4 inch thick. Particulates are retained on the cartridge for removal.
Chelant	A chemical compound that ties up iron, copper or calcium to prevent scaling and staining. Also called a sequestering agent.
Chemical Feeder	A mechanical device that dispenses chemicals in pool water.
Chloramines	Substances formed when chlorine combines with swimmer wastes (nitrogen or ammonia), causing chlorine odor and irritation to skin and eyes. This compound has little sanitizing value compared to active chlorine.
Chlorinator	A device that dispenses chlorine into pool water in a controlled, gradual manner.
Chlorine	The most widely used bacteria-killing agent for pool water. Organic chlorine is more suitable than inorganic for pool use because it is generally easier to use, does not affect water balance as much and is non-clouding. See also Hypochlorite
Chlorine Demand	The amount of chlorine addition required before a free chlorine residual can be maintained.
Chlorine Generator	On-site equipment that generates its own supply of chlorine, hypochlorous acid or hypochlorite for pool use.
Chlorine Neutralizer	Sodiumthiosulfate or other compound used to neutralize excessive chlorine in water sample. This permits accurate testing for pH and total alkalinity.
Chlorine Residual	The amount of chlorine left to kill new bacteria entering the pool after it has been sanitized. It is the chlorine level present after chlorine demand has been satisfied.
Clarity	The degree of transparency of pool water.
Coagulate	Using a chemical compound to gather suspended particles together in pool water for more effective filtration.
Combined Chlorine	Chlorine that is in combination with ammonia, nitrogen or other organic compounds. See chloramines.
Corrosion	Etching, pitting, and other destructive erosion of pool surfaces and equipment due to low pH or other chemical imbalance.
Cyanuric Acid	A chemical added to pool water to reduce degradation of chlorine by sunlight. Also called a stabilizer, conditioner and isocyanuric acid.
top D
Diatomaceous Earth (DE)	A powdery filtering agent composed of microscopic prehistoric diatom skeletons. Also called diatomite.
Diatomaceous Earth Filter	A filter that uses diatomaceous earth or volcanic ash as a medium.
Disinfectant	Chlorine or other sanitizer that kills disease-causing bacteria in pool or spa water.
DPD (Diethyl-P-Phenylene Diamine)	A test reagent used to measure the amount of available chlorine in pool water. It measures both total and free chlorine. See also Orthotolidine (OTO)
top E
Effluent	Water flowing out of filter or other device.
top F
Filter	A device that removes waste particles from the pool as water circulates through a porous substance called a filter medium.
Filter Aid	Diatomaceous earth, volcanic ash or other powdery substance used to coat a septum or sand filter.
Filter Cartridge	A porous, disposable element used as a filter medium.
Filter Cycle	The operating time between backwash cycles.
Filter Element	A porous component in the filter tank that removes particles and other suspended wastes from water before its re-circulated back to the pool.
Filter Medium	Sand, diatomaceous earth, anthracite or other finely graded material used to filter particles out of pool water.
Filter Sand	Sharp silica or quartz particles graded for uniform size and used as a filter medium.
Floc	A filterable gel that forms when alum combines with suspended particles in pool water.
Flow Meter	A measuring device that determines the gallons per minute of water flow through a pool re-circulation system.
Flow Rate	The volume of liquid flowing past a given point in a specific time period, expressed in gallons per minute or hour. See Filtration Flow and Filtration Rate
Free Available Chlorine	Hypochlorous acid, the chlorine in pool water that is not combined with ammonia or nitrogen and therefore available to kill bacteria entering the pool.
top G
top H
Halogens	Refers to the active chemical elements: chlorine, bromine, fluorine, and iodine.
Hydrochloric Acid	A strong acid used to control pH in pools and to acid wash pool interiors. It is also called muriatic acid. Use with extreme caution, employing proper safety equipment.
Hydrogen	Combines with oxygen to form water. In its ionic form, in solution, it measures as pH.
Hypobromous Acid	The most effective form of bromine in water for disinfecting.
Hypochlorite	An inorganic un-stabilized family of chlorine compounds used in various forms to provide chlorine for pool water. Includes calcium hypochlorite, lithium hypochlorite and sodium hypochlorite.
Hypochlorous Acid	The active sanitizing form of chlorine.
top I
Influent	The water entering a filter or pipe.
top J
top K
top L
Liquid Acid	Muriatic acid added to pools to lower pH and total alkalinity.
Liquid Chlorine	Sodium Hypochlorite (NaOCI) solutions added to the pool as a disinfectant.
top M
Make-Up Water	Fresh water used to fill the pool or top it off to the usual level. Also called source water.
Muriatic Acid	Hydrochloric acid added to pool water to decrease pH and total alkalinity. It can also be used with caution to acid wash pool interiors.
top N
Nitrogen	An element that combines with chlorine to form chloramines, which causes swimmer irritation and chlorine odor.  enters pool water from cosmetics, perspiration, and other swimmer wastes.
top O
Organic Chlorine	A form of chlorine that contains carbon and hydrogen atoms. The most common ones for pool use are sodium dichloroisocyanurate (also know as sodium dichlorostriazinetrione) in granular form and trichloroisocyanurate (also known as trichlorostriazinetrione) in compressed form.
Organic Matter	Pool contaminants derived from living organisms. These include leaves, suntan lotions, cosmetics, urine, perspiration and other swimmer wastes and environmental debris.
Organisms	Algae or bacteria that grow in pool water.
Orthotolidine (OTO)	A test reagent used to measure the total amount of chlorine in pool water. In the presence of chlorine, it turns yellow to amber in color.
Oxidation	A chemical process for removing irritating organic compounds from pool water. It also refers to the rusting or corrosion process that occurs as metals weathers.
Oxidizers	Agents that help eliminate organic waste from pool water.
top P
pH	A measurement that indicates the acidity or alkalinity of pool water. On a scale of 0 to 14, values below 7 are acidic, while values above 7 are alkaline. Ideal pool pH is a reading of 7.4 - 7.6.
Phenol Red	A dye for measuring the pH of water from 6.8 to 8.4. It changes from yellow to purple in color.
ppm	Parts per million, a unit of measurement used in chemical application. It indicated the amount, by weight of a chemical in relation to one million parts by weight of water (examples: 1 minute in 2 years, 1 inch in 16 miles, or 1 penny in $10,000). Equivalent to milligrams per liter (mg/L).
Precipitate	Solid particles forced out of solution by a chemical reaction. They may settle to the bottom of the pool or remain suspended in the water.
Pump	A motor-powered mechanical device that creates pressure and water flow to permit filtration, heating and water circulation. Pools usually use a centrifugal-type pump.
Pump Strainer	A lint and hair trap on the suction side of the pump to remove debris with a minimum of water flow restriction.
top Q
top R
Reagents	Chemical test solutions that can be used to check water for chlorine, pH, total alkalinity and other factors.
Re-circulation System	The pipes, fittings, filters and pumps through which water circulated in and out of the pool.
Residual	The amount of measurable chlorine in pool water after it has been sanitized. Free residual is not combined with ammonia or other compounds, resulting in a more effective disinfectant that combines chlorine. See Chlorine, Free Available Chlorine
top S
Sand Filter	A pool filter that uses sand or sand and gravel as a filter medium.
Saturation Index	A numerical value used to indicate whether pool water is out of balance (either scale-forming or corrosive). Four factors are taken into account: pH, total alkalinity, calcium hardness and water temperature.
Scale	Hard deposits that form on pool surfaces and equipment due to excessive calcium in the water (calcium carbonate).
Sequestering Agent	- See Chelant
Shock Treatment	An extra large dose of chlorine applied every two weeks or as needed to kill algae and eliminate chloramines in the water.
Skimmer	A device in the pool wall that continuously directs debris and surface water to the filter. A hand skimmer can be used manually to collect leaves and other large floating debris from the water’s surface.
Soda Ash	Sodium Carbonate added to pool water to raise pH.
Sodium Bicarbonate	A pool additive (baking soda) used to raise total alkalinity.
Sodium Hypochlorite	Inorganic chlorine in clear, liquid form.
Sodium Dichloroisocyanurate	A granular organic chlorine that contains 62% available chlorine. Also known as sodium dichloro-s-triazinetrione.
Sodium Thiosulfate	A chemical used to prevent false pH readings. It is added to the water sample to remove chlorine prior to testing.
Soft Water	Water that contains less than 100 ppm of calcium and magnesium.
Stabilizer	See Cyanuric Acid
Super Chlorination	See Shock Treatment and Breakpoint Chlorination
top T
Test Kit	An assortment of reagents used to test pool water for pH, chlorine residual and total alkalinity.
Titration	A method of testing pool water for calcium hardness and total alkalinity.
Total Alkalinity	The amount of alkaline bicarbonate in pool water. It acts as a buffer to prevent fluctuations in pH.
Total Dissolved Solids	The total amount of dissolved calcium, magnesium, carbonates, salts and other substances in pool water.
Trichloroisocyanurate	An organic chlorine available in compressed tablets or sticks, containing 90% available chlorine. Also known as trichloro-s-triazinetrione.
Turbidity	Cloudy condition of water caused by finely divided microscopic material in suspension interfering with the passage of light.
top U
top V
top W
Winterizing	The procedure for protecting pools, spas and hot tubs from freezing conditions. It includes physical and chemical protection of the pool or spa and its equipment against freezing.
top X
top Y
top Z