Glossary of Terms

A

B

C

D - G

H

I - O

P - R

S - Z

Acid - A chemical compound which releases hydrogen ions into water, decreasing pH. Products like muriatic acid or Lo 'N Slo are used to lower pH and Total Alkalinity in pool water.

Acid Demand - The amount of acid needed to lower pH to the proper level for pool water.

Aeration - The process of mixing air and water. In a spa this can happen two ways: 1) Using an Air Blower to force air into an air channel or through the spa jets. 2) With Venturi Air Controls which allow air to be pulled into and mixed with the water the spa jet.

Algae - Microscopic plants deposited in pool or spa water by wind, rain, and dust. They thrive in sunlight and warm water, clogging filters, increasing the need for sanitizers and oxidizers, and causing slippery surfaces. There are 21,000 known species of algae.

Algicide - A chemical added to water to kill algae infestations and prevent their recurrence.

Algistat - Any substance that retards algae growth.

Alkali - A basic solution that neutralizes acids.

Alkali Demand - The amount of alkali (base) needed in the water to raise pH and/or Total Alkalinity to the proper level.

Alkaline - When the pH of a solution measures above 7.0 on the pH scale. Alkaline (often referred to as "basic") is the opposite of acid.

Ammonia - A nitrogen-containing compound that combines with free chlorine to form chloramines.


Backwash - Reversing the flow of water through the filter to clean the elements and filter medium. Typical maintenance for sand filters and some DE filters.

Backwash Cycle - The time needed to backwash (clean) the filter and its components.

Bacteria - Single-celled microscopic organisms. Pathogenic bacteria can cause infections, disease and bather irritation. Chlorine and Bromine are used to kill bacteria in pool & spa water.

Balanced Water - Pool or spa water that has a proper pH and the appropriate mineral content to prevent corrosion and scaling.

Base - See Alkali.

Bather - In a Spa, a bather is anyone using a spa for a duration of 20 minutes at 102 F.

Bather Load - The number of people in a pool or spa at a particular time or during a specific period of time.

Biguanide - A long chain polymeric molecule with both bactericidal and algicidal characteristics (such as SoftSwim® B). Must be used in pool maintenance with a supporting oxidizer (such as SoftSwim® C).

Biofilm - The accumulation and/or colonization of bacteria, algae, mold, fungus and other micro organisms on the surface of the pool/spa.

Borate - An elemental mineral used for conditioning water to provide clearer, more comfortable water.

Breakpoint - During chlorination, this is the point at which all combined chlorine is oxidized (removed) and only Free Available Chlorine remains in the water to kill bacteria. This point is achieved when Free Available Chlorine is 10 times higher than Combined Chlorine.

Bromamines - Non-irritating bromine-ammonia compounds that have some degree of sanitizing capabilities.

Bromide - An inactive ion that can be activated to hypobromous acid by some means of oxidation, either with chlorine, ozone, or oxidizing shock.

Bromine - A chemical used in various compound forms to kill bacteria in pool & spa water. Hypobromous Acid is the active killing agent that all bromine compounds form when dissolved in water.

Buffer - Chemicals that serve to prevent fluctuations in pH (see Total Alkalinity).

Calcium Carbonate - Scale that forms from calcium compounds when pool water is too 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. Low levels of calcium hardness will promote deterioration in the pool surfaces and equipment. High levels will promote scale formation.

Calcium Hypochlorite
- A chlorine compound using calcium as the carrying salt for application.

Cartridge - A porous, replaceable element in some filters. Particulates are removed when they penetrate into the medium. Particulates are retained on the surface of the cartridge for removal. Loose debris can be hosed off, oils must be chemically removed by soaking the cartridge.

Chelant - A chemical compound that 'ties-up' iron, copper, or calcium to prevent staining and scaling. Also called a sequestering agent.

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.

Chlorine - One of five members of the Halogen family of chemical elements. It is the most widely used bacteria-killing agent for recreational water treatment. Two forms of chlorine are used: (1) Organic chlorine - less vulnerable to the UV rays of the sun and therefore longer lasting. (2) Inorganic chlorine- susceptible to degradation by the UV rays of the sun and therefore less convenient for pool use. Also see Hypochlorite.

Chlorine Demand - The amount of chlorine required to be added to the water before a free chlorine residual can be maintained. Both dissolved and undissolved organic and inorganic debris can contribute to a chlorine demand.

Chlorine Generator
- On-site equipment that generates its own supply of chlorine, hypochlorous acid or hypochlorite for water treatment. The chlorine is typically generated from Sodium Chloride (salt) by exposing it to a low voltage (DC) electrical current.

Chlorine Neutralizer - A compound used to neutralize excessive chlorine in a water sample in order to permit more accurate testing of the water balance factors. It can also be used in the pools and spas themselves to neutralize high levels of Chlorine or Bromine.

Chlorine Residual - The amount of chlorine left to kill new bacteria entering the pool after is has been sanitized. It is the chlorine level present after the chlorine demand has been satisfied.

Coagulant - A polymeric chemical compound added to water to gather suspended particles together for filtration. SpaGuard Water Clarifier and PolySheen Blue are coagulants.

Combined Chlorine - Chlorine that is in combination with ammonia, nitrogen, or other organic compounds. See Chloramines.

Contaminated - An impure condition indicating the presence of bacteria, algae or other undesirable matter in water.

Corrosion - Etching, pitting and other destructive erosion of the spa surfaces and equipment due to low pH or other chemical imbalance.

Cyanuric Acid - A chemical compound added to pool water to reduce the degradation of chlorine by the UV rays of the sun. Also referred to as CYA, stabilizer, and conditioner.

Diatomaceous Earth (DE) - A powdery filtering agent composed of the skeletal remains of a form of plankton (diatoms). Used in Diatomaceous Earth filters.

DPD #1 - A test reagent (typically a tablet) used to measure the amount of Free Available Chlorine or Total Bromine in the water.

Dry Acid - Safer to handle than Muriatic Acid, it lowers the pH or Total Alkalinity. Lo N Slo® is a dry acid.

Effluent - The water that flows out of a filter, pump or other device.

Filter - A device that removes undissolved particles from water through a porous filter medium (sand, cartridge, DE).

Filter Cycle - The operating time between filter cleaning or backwash cycles. Long filter cycles are the most convenient.

Filter Element - A device (cartridge) within a filter tank designed to entrap solids and allow the flow of water through the filter back to the spa.

Filter Medium - Sand, Diatomaceous Earth, or other finely graded material used to filter particles out of the water.

Filter Sand - Sharp silica or quartz particles graded for uniform size and used as a filter medium. #20 Silica Sand is the industry standard grade of filter sand.

Flocculant - A chemical compound added to water causing suspended particles to sink. Once on the bottom of the pool the once suspended particles can now be vacuumed to waste.

Flow Meter - A measuring device that determines the gallons per minute of water flow through a pool circulation system.

Flow Rate - The volume of liquid (water) flowing past a given point in a specific time period, expressed in gallons per minute.

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 water. See also Available Chlorine.

Gelcoat - The colored surface layer of a fiberglass pool or spa shell. This resin is applied to the mold during the manufacturing process.

Gunite (shotcrete) - A concrete and sand mixture sprayed into a reinforced steel form to create a pool shell. Plaster, paint, or some other form of cosmetic finish is applied on top of the gunite structural shell.


Halogen - A family of chemical elements containing Chlorine and Bromine, and widely used for a variety of sanitizing situations.

Hot Tub - A wooden vessel, containing hot moving water. First popularized on the west coast by cutting wine barrels in half, the hot tub market rose and fell in popularity with the advent of vacuum formed thermoplastic materials. Mass production of Hot tubs has employed the use of varied types of wood from redwood, cypress, teak, and other exotic tropical hardwoods.

Hydrogen Ion - The positively charged nucleus of a hydrogen atom. Increasing levels of the hydrogen Ion in the water will cause pH to be lowered.

Hydrogen Peroxide - An oxidizing solution typically used as a liquid shock treatment and clarifier for biguanide pools.

Hydrotherapy Jets
- A spa fitting that blends air and water creating a high-velocity, turbulent stream of air enriched water.

Hydrotherapy Spa - A non-wooden vessel containing hot moving water for therapeutic use to ease stress, muscle strains and other physical problems. Popular construction types include thermoplastic shells and gunite/plaster interiors.

Hypobromous Acid - The most effective form of bromine in water for disinfecting.

Hypochlorite - An inorganic (unstabilized) family of chlorine compounds used in various forms to provide chlorine for water treatment. Includes calcium hypochlorite, lithium hypochlorite, and sodium hypochlorite.

Hypochlorous Acid - The active sanitizing compound formed when any type of chlorine is put in water.

Impeller - The "heart" of the centrifugal pump. Rotating veins create the suction flow of the water into the pump.

Influent - The water entering a pump, filter, heater, or pipe.

Inorganic Chlorine (Unstabilized Chlorine) - A form of chlorine that is vulnerable to degradation to the UV rays of the sun. See Hypochlorite for forms of unstabilized chlorine.

Leaching - The process of extracting a mineral from plaster interiors or tannic acid from wooden hot tubs.

Liquid Chlorine - Sodium Hypochlorite solutions added to water as a disinfectant. Characteristics include very low levels of available chlorine, high contribution to Total Dissolved Solids, a high pH, and inconvenient to apply and handle. Should not be confused with Clorox® with even lower levels of available chlorine.

Make-Up Water - Fresh water used to fill the pool or spa. Also called Source water.

Muriatic Acid - See acid.

Nitrogen - An element that when combined with chlorine forms chloramines. Common in rainwater, cosmetics, oils, perspiration, and urine.

Organic Chlorine - A form of chlorine that contains cyanuric acid/stabilizer/conditioner.

Organic Matter - Contaminants derived from living organisms. Including leaves, cosmetics, urine, perspiration, bugs, animals, and other bather/environmental debris. Organic compounds are any which contain carbon.

Orthotolidine (OTO) - A test reagent used to measure the amount of Total Chlorine in pool water. In the presence of increasing levels of chlorine it turns yellow to amber in color.

Oxidation - A chemical process for removing breaking down organic compounds.

Ozone - A gaseous molecule composed of three atoms of oxygen. Ozone is
created for oxidation of water contaminants. Its instability and short life in the water require that it be used only to supplement chlorine or bromine to control bacteria.


pH (potential Hydrogen) - A measurement that indicates the acidic or basic nature of a solution. Measured on a scale from 0 to 14, the ideal pH of pool/spa water should be 7.4 to 7.6. A pH of 7.0 is neutral. A pH below 7.0 is acidic. A pH above 7.0 is basic.

Phenol Red - A reagent (dye) for measuring the pH of water in a range from 6.8 to 8.2. It changes color from yellow to purple in color as the pH goes from 6.8 to 8.2.

Plaster - The interior finish of a gunite (concrete) pool or spa. Usually composed of white marble dust and portland cement.

ppm - Parts per million, a unit of measurement used in measuring chemical application. It indicates the amount, by weight, of a chemical in relation to one million parts by weight of water.

Psi - Pounds per square inch. The unit by which filter pressure is measured on a pressure gauge. Psi increases as the filter gets dirtier.

Precipitate - Solid particles forced out of solution by a chemical reaction. They may settle on the bottom of the pool or spa, or remain suspended in the water giving the water a cloudy look.

Precoat - The coating of Diatomaceous Earth placed on the grids/fingers of a DE filter at the beginning of each filter cycle.

Pump - A motor-powered mechanical device that creates pressure and water flow by spinning an impeller to provide circulation through the filter other system components. Some spas combine a pump for filtration/heating with an additional "'therapy pump".

Reagent - Chemical testing compounds that are used to test for chlorine, bromine, pH, total alkalinity, calcium hardness, etc.

Saturation Index (SI) - A numeric value indicating whether water is scale forming or corrosive. It factors in pH, Total Alkalinity, Calcium Hardness, and water temperature.

Scale - Mineral deposits that form on pool and spa surfaces and equipment due to excessive calcium in the water. Scale is more likely to form in heated water, especially on the heater element or heat exchanger, if proper water balance is not maintained.

Shock Treatment - The addition of an oxidizing compound to the water to chemically break-up (oxidize) contaminants such as suntan oils, cosmetics, perspiration, metal ions and wind-blown dirt which interfere with normal sanitizer performance and/or cause cloudy or colored water.

Skimmer - A device in the pool or spa wall that continuously removes the surface water and floating debris to be taken away by the filter. A hand skimmer net can be used manually to "dip" large floating debris from the water.

Sodium Bicarbonate - Added to water to increase the Total Alkalinity. The water treatment grade of Sodium Bicarbonate is used in pool water. The baking grade (baking soda) is used for cooking. The two grades do not share the same physical characteristics, and should not be interchanged.

Soft Water - Water that contains less than 100 ppm of calcium and magnesium.

Superchlorination - The addition of a sufficient amount of chlorinating compound (usually 3 to 5 times the usual dosage) to the pool water for the destruction of chlorine demand compounds and any combined chlorine which may be present.

Stabilized Chlorine - An organic chlorine compound used to sanitize pool water and favored for its economy and ability to remain active in the presence of strong sunlight. (NOTE: non-stabilized chlorine such as liquid chlorines or drum chlorines are rapidly lost in water when exposed to sunlight.

Stabilizer - Cyanuric acid; a compound that prevents the dissipation of chlorine to the ultraviolet spectrum of the sun, BioGuard Stabilizer 100.

Surfactant - The word surfactant comes from its description: Surface Active Agent. It applies to any chemical compound that can decrease the surface tension of a liquid (water). When you add a surfactant to pool water, it helps the water penetrate the cracks and crevices where algae hide (and of course, the water brings the FAC and any other algae-killing chemicals with it).

Total Alkalinity - A measure of the water's ability to resist pH change due to the presence of these compounds in the water.

The information on this page has been provided courtesy of BioLab, Inc. ©1998