Common Hot Tub Terms and Definitions

Acid – A chemical used to lower the pH of pool or spa water. Available in liquid (muriatic or hydrochloric acid) and granular (dry acid or sodium bisulfate) forms.

Algae – Microscopic plant life found in abundance in nature. Can grow in swimming pools and damage surfaces and clog equipment.

Algicide / Algaecide – A chemical used to kill algae or prevent algae growth.

Alkalinity – See Total Alkalinity.

Backwashing – Reversing the water flow through a sand filter or D.E. filter to clean it. D.E. filters require reapplication of D.E. (Diatomaceous Earth) after backwashing.

Bacteria – Typically one-celled microorganisms which multiply by simple cell division. Some can cause infections such as pseudomonas. All can eventually cause sanitizer demand and cloudy water.

Bactericide – A product added to the water which kills bacteria.

Balanced Water – Water that has the proper ratio of mineral content and pH to prevent corrosion and scaling.

Bather Load – The ratio of people in a pool or spa compared to the amount of water.

Bicarbonate Scale – Scale buildup comprised mostly of bicarbonates, rather than calcium carbonate. Bicarbonate scale occurs in pool settings most often when there is poor offgassing due to insufficient ventilation. Gasses that normally evaporate from bodies of water are reabsorbed into the pool and cause the pH to decrease, the total alkalinity to increase, and cloudy water as the scale falls out of solution.

Biguanide – The active ingredient used in many chlorine alternatives, including Baquacil and SoftSwim.

Broadcasting – Distributing chemicals in the pool by scattering over the water surface.

Bromine – A halogen disinfectant. Bromine cannot be stabilized against ultraviolet light. It is ideal for use in spas and indoor pools.

Calcium Hardness – The amount of dissolved calcium in the water. Low residuals can cause etching and corrosion in pools, while high residuals can cause scale buildup and cloudy water.

Cartridge Filter – A pool or spa water filter that uses paper or fabric-like pleats as a filtering agent.

Chloramines – Also called combined chlorine. Irritating compounds formed by the combination of nitrogenous compounds and free chlorine. Nitrogenous compounds are introduced into the water by things like urine, perspiration, cosmetics, and suntan oils.

Chlorine – A halogen sanitizer. Manufactured in organic (stabilized) and inorganic (unstabilized) forms. Can be used to effectively sanitize pools and spas.

Chlorine Demand – The amount of free available chlorine residual needed to destroy undesirable compounds and establish a stable free chlorine residual for effective sanitation.

Chlorine Residual – The amount of a chlorinating product (total or free chlorine) in pool water measured in parts per million (ppm).

Cyanuric Acid – A compound that prevents the dissipation of chlorine residuals by sunlight.

D.E. (Diatomaceous Earth) Filter – A water filter which uses diatomaceous earth (tiny prehistoric diatom skeletons) as a filter media. These skeletons are very porous and provide an excellent filter media.

Filter – A device that removes particles as water passes through the medium. Most pool and spas filter media are either cartridge, diatomaceous earth (D.E.), or sand.
see also Glossary of Filtration Terms

Free Available Chlorine (FAC) – Chlorine residual in a form capable of bacteria and algae destruction.

Make-Up Water – Fresh water used to top off the pool or spa to the normal level.

Muriatic Acid – A liquid chemical used to lower the pH of water.

Organic Matter – Contaminants derived from living organisms. Leaves, grass, urine, perspiration, and other swimmer wastes as well as cosmetics and environmental debris fall under this description.

Oxidation – The chemical recation that releases nitrogen from a chlorine molecule and eliminates certain undesirable compounds from pool water.

Oxidize – Adding an oxidizing compound to the pool water to chemically break up (oxidize) contaminants such as suntan oils, cosmetics, perspiration and windblown dirt. Burn Out Extreme and SoftSwim C are examples of oxidizing compounds.

pH – A measure of the acidity or alkalinity of water. pH is an arbitrary scale from 0 – 14, with 0 being most acidic, 7 being neutral, and 14 being most alkaline. Ideal pH for bather comfort and equipment maintenance range from 7.4 – 7.6.

Polymer – A compound made up of large, long chain molecules of many repeated simple units. SoftSwim B and Polysheen Blue are polymeric based.

ppm – parts per million. A measurement for chemical concentration.

Reagent – Tablets, powder or liquid material for use in water testing.

Sand Filter – A water filter which uses fine silica sand as a filter media.

Saturation Index – A value based on water temperature, total alkalinity, total hardness, and pH. The value predicts the tendency of pool water to be corrosive, neutral, or scale-forming. For in season water temperatures, an index below -0.3 tends to be corrosive, while an index above +0.3 indicates scale forming potential.

Scale – Calcium or silicate deposits on swimming pool walls, floors and circulation plumbing, including heat exchangers.

Shocking, Shock Treatment – See Oxidize.

Stabilized Chlorinating Products – A form of chlorinating compound used to sanitize pool water. Favored for its economy and ability to remain active in strong sunlight.

Stabilizer – See Cyanuric Acid

Superchlorinate – Adding enough chlorinating compound to destroy chlorine demand compounds and combined chlorine.

Total Alkalinity – The amount of the alkaline components in the water. Total alkalinity measures acidity and alkalinity of water as does pH, but is slightly different. The total alkalinity acts as a buffer against rapid pH fluctuation. High total alkalinity can cause scale buildup and cloudy water, and causes the pH to drift up and increase the difficulty in adjusting pH. Low total alkalinity causes water to be corrosive and causes pH to drift down. pH adjustments made to water with low total alkalinity often cause the pH to bounce.

Total Hardness – The total amount of dissolved minerals, (calcium and magnesium) in the water as measured in ppm.

Undesirable Compounds – Substances introduced into the water by people or the environment that interfere with ideal water balance conditions.

Winterizing – The process of closing down a pool or spa for the inactive off-season and protection from freezing. Usually includes chemical treatments of the water and physical protection of the equipment.