Swimming pool treatment has its specific vocabulary. We have decided to produce this glossary to help you understand the commonest terms specific to swimming pool treatment. Click on a letter below to view a term.

A

Acidity

The quality of being acidic (corrosive) as opposed to the quality of being basic; any measurement below neutral pH (7.0) on the pH scale.

Acid required

The quantity of acid required to reduce the pH and total alkalinity of swimming pool water to reach the correct level.

Aggressive water

Acidic and unbalanced water that etches and corrodes the surfaces, accessories and pipework of swimming pools.

Algae

Forms of single-cell or multicellular microscopic plant life. They need sunlight to reproduce. They are found in vegetation, in the air, in soil and in water. Their microscopic pores constantly get into the swimming pool in the wind, dust storms, rain showers etc. They grow rapidly in swimming pool water when exposed to sunlight and at temperatures above 4.44 °C (40 °F). If they are not removed by chemical treatment they end up forming a viscous substance that tends to spread over the entire surface of the water, giving off a foul smell. They can impair the normal process of filtration and considerably increase the quantity of chlorine required. Phosphates present in the water encourage them to grow.

Algicide

A chemical agent specifically developed and used to kill algae.

Alkalinity

Alkalinity corresponds to the quantity of bicarbonates, carbonates and hydroxides in the water. It is a measurement of the water's buffering capacity (the degree of its resistance to variations in pH).

Alum

An aluminium sulphate compound that enables solids suspended in (swimming pool) water to clump together so that it can be filtered out (flocculant).

B

Bacteria

Invisible single-cell organisms of different forms, some of which can cause infection or illness.

Balanced water

Water that contains only the required quantities of calcium hardness, total alkalinity, pH and dissolved solids to prevent the tendency of the water to form lime scale and be corrosive.

Basicity

The quality of being basic (alkaline) as opposed to the quality of being acidic; any measurement above neutral pH (7.0) on the pH scale.

Bromine = Chlorine free

Disinfectant used in a similar way to chlorine.

C

Calcium

A precipitate that forms on surfaces in contact with the water when the pH, alkalinity and calcium hardness are too high.

Calcium hardness

Measurement of the quantity of calcium dissolved in the water. The recommended range is 200 to 1,000 ppm.

Calcium chloride

Soluble white salt used to increase the calcium hardness of swimming pool water when required.

Calcium hypochlorite

Disinfectant and chlorinator that contains no stabilisers.

Chloramines

Compounds formed when chlorine combines with nitrogen compounds derived from anatomical waste such as perspiration, urine and skin proteins. Chloramines give off a very unpleasant strong smell of chlorine and can irritate the eyes of bathers and cause skin irritation.

Chlorine

One of the five halogen elements and the one most commonly used (in various forms) to disinfect water. A disinfecting element available in granule and tablet form and also as gaseous chlorine.

Chlorine lock

Term used in the profession to describe a situation in which chlorine removes algae, bacteria and organic matter less quickly. This situation is caused by overstabilisation, in other words an excessive quantity of cyanuric acid.

Chlorine residue

See Free residual chlorine.

Clarifier

A chemical used to clarify cloudy water by causing the small particles present in the water to clump together to form larger clumps of particles. This makes it easier for the filter to remove them.

Combined chlorine

Chlorine that is bound to or combined with nitrogen compounds in the form of chloramines.

Corrosive water

State of water that has a low pH (acidic state) and that may corrode the pipework and accessories of swimming pools and metal pumps. Can also etch plastic and cause eye irritation.

Cyanuric acid

A chemical capable of preventing the evaporation of chlorine due to sunlight. Cyanuric acid protects the chlorine from destruction caused by ultraviolet radiation and releases chlorine when required. It is the essential ingredient in hth Stabilizer.

D

Diatomaceous earth

Filtration agent made up of the tiny skeletons of diatoms (single-cell organisms).
 

Disinfectant

Generic term for a substance used as a sanitising agent to remove algae and bacteria and oxidize organic contaminants. Substances containing chlorine are often used as disinfectants.

DPD

Dimethyl-p-phenylenediamine: A reagent and test method used to measure the quantities of free residual chlorine and total chlorine.

F

Feeder

Device located by the swimming pool's circulating water pipe that provides a constant, controlled supply of chlorine, generally in tablet-form, to the recirculating water.

Filter

Device located by the swimming pool's circulating water pipe that intercepts solid contaminants by passing the water through a filtering medium. The most frequently used media are sand, diatomaceous earth and cartridges.

Filtration system

The medium used in a filter to intercept the solids responsible for both the cloudy and the dirty appearance of the water.

Floater

Device that floats on the surface of the swimming pool water and contains a dose of chlorine (generally in tablet form) that is released into the water for a set period of time.

Flocculant

Used as an agent that causes solids suspended in the water to clump together so that they can be filtered out.

Free residual chlorine

(Also known as chlorine residue or residual chlorine.) The quantity of active chlorine that remains in the water once the volume of chlorine required to eliminate algae, bacteria and other contaminants has been reached. The recommended amount of free chlorine is 1.5 to 4.0 ppm. This amount provides protection against other contaminants likely to come into contact with swimming pool water.

Fresh water

Water with a low mineral content (calcium and magnesium).

H

Halogens

Group of five elements (chlorine, bromine, iodine, fluorine and astatine), the first three of which are active ingredients in almost all disinfecting products.

Hardness

Quantity of calcium and magnesium dissolved in the water. High levels of hardness encourage the formation of cloudy water and lime scale, whereas low levels make it more likely that the water will damage parts of the swimming pool. Calcium hardness is used to ensure that the water is balanced.

Hydrochloric acid (muriatic acid)

Hydrogen chloride (HCl) solution is used to reduce the pH and/or total alkalinity of swimming pool water. Also used to acid-wash swimming pools containing cement, plaster or gunite, hydrochloric acid is not advised for swimming pool water treatment because it causes an imbalance in the water, affecting alkalinity among other things.

I

Isocyanurates

Family of chlorinated products for swimming pools that are self-stabilising owing to the cyanuric acid they contain. Available in tablet and granule form.

L

Langelier index

See saturation index.

Liquid chlorine (not stabilised)

Aqueous solution of sodium hypochlorite. It is commonly called bleach. Present in residual chlorine at levels of between 3 and 5% (domestic bleach) and between 10 and 15% (bleach used in swimming pools or for industrial use).

O

OTO

Orthotolidine. Colourless reagent that reacts with chlorine to produce a whole series of colours from light yellow to dark orange, indicating the quantity of chlorine in the water. Cannot be used to measure the total chlorine.

Overchlorination

Practice of adding a sufficient quantity of chlorinated products to the water in order to remove undesirable compounds and all the combined chlorine likely to be present. In general, the level of added chlorine is 10 times as high as that of the combined chlorine in the water.

Overflow channel or skimmer

Surface sieving device located by the overflow channels and points of a swimming pool which intercept leaves and other floating debris. It is often used to add chemicals, particularly in tablet form, to the recirculating water.

Overstabilisation

Formation of cyanuric acid in swimming pool water generally caused by the combined intensive use of long-lasting stabilised organic chlorines and stabilised shock products.

Surface sieving device located by the overflow channels and points of a swimming pool which intercept leaves and other floating debris. It is often used to add chemicals, particularly in tablet form, to the recirculating water.

Oxidise

To eliminate solids, colours and undesirable odours.

P

pH

Measurement of the acidity or basicity of swimming pool water on a scale from 1 to 14. A low pH indicates an acid state which will result in bather discomfort and can corrode any swimming pool equipment containing plaster or metal. On the other hand, a high pH indicates a basic state, which encourages the formation of cloudy water and lime scale. The desirable pH for swimming pool water is between 7.0 and 7.4.

Phenol red

Colourant sensitive to differences in pH. Turns yellow if the pH is acidic, red-violet if the pH is high and orange if the pH is neutral.

pH Minus

hth brand name for hydrogen sulphate (also known as dry acid). It is used to reduce the pH and/or total alkalinity of swimming pool water.

pH Plus

hth brand name for sodium carbonate (Na2CO3, also known as soda ash. It is used to increase the pH.

PPM

Parts per million. Parts (weight) of a chemical or mineral per million parts of/in water.

Precipitate

Solid extracted from a solution through a specific chemical reaction and which forms a deposit.

Purity

State of sanitation obtained following suitable treatment using disinfectants that remove dangerous microorganisms such as algae and bacteria.

Q

Quats (Quaternaries)

Quaternary ammonium salt. Type of nitrogen compound used as an algicide and disinfectant.

R

Required chlorine

Quantity of chlorine required to remove algae, bacteria and other contaminants from swimming pool water. Once the quantity of required chlorine has been reached the water is considered to be disinfected until another contamination occurs.

Residual chlorine

An amount equal to the total chlorine content of a chemical (its oxidising ability), by comparison with elemental chlorine (a gas), which contains 100% residual chlorine.

S

Saturation index

Formula that uses the numerical values allocated to each of the five "balanced water" factors to generate an index number used to determine and adjust the balance of swimming pool water. The five factors are pH, temperature, total alkalinity, calcium hardness and total dissolved solids. An index result of between -0.5 and +0.5 is considered to be suitably balanced.

Shock treatment

Addition of chlorine in much bigger proportions than normal in order to remove elements affecting the quality of the water: algae, bacteria, chloramines, discoloured water, etc.

Soda (bicarbonate of)

See Sodium acid carbonate

Soda ash

See Sodium hydrogen carbonate

Sodium Hydrogen Carbonate
An alkaline compound (NaHCO3) used to increase total alkalinity. Should not be used for increasing the pH.

Sodium acid sulphate or sodium bisulphate

Dry acid (NaHS04). One of the ingredients of hth pH Minus. It is used to reduce the pH and/or total alkalinity of swimming pool water.

Sodium bicarbonate

See Sodium hydrogen carbonate.

Sodium carbonate

Soda ash (Na2CO2) An ingredient in hth pH Plus. Increases the pH.

Spores

Tiny seeds produced by many forms of plant life, particularly algae.

Stabilised chlorine

See Isocyanurates.

Stabilised swimming pool

Swimming pool treated with cyanuric acid or stabilized chlorine to reduce chlorine evaporation due to sunlight.

Stabiliser

See Cyanuric acid. Reduces the dissipation of chlorine throughout the swimming pool caused by the effect of sunlight. (The hth brand name for this product is hth Stabilizer.)

Surface spreading

Method that involves spreading granulated or powdered chemicals thinly all over the surface of the swimming pool water.

T

TCCA

Trichloroisocyanuric acid, trichloro-s-triazinetrione. This is the active ingredient in tabs and hth LARGETABLET. See Isocyanurates.

Total alkalinity

Measurement of the total alkaline substances dissolved in the water. If it is too high, the pH is more difficult to adjust. On the other hand, if it is too low the pH tends to fluctuate considerably (very irregularly).

Total chlorine

A measurement of the free chlorine plus combined chlorine in swimming pool water.

Total dissolved solids

Measurement of all of the solids dissolved in the water. If this is too high it can give the water a dark appearance and a flat, salty taste.


W

Water analysis kit

Kit used to analyse the factors that determine the balance of swimming pool water.

Water softener

A chemical that replaces calcium or magnesium with sodium or potassium to prevent these substances making marks around the swimming pool. Not recommended for filling swimming pools.

Winterising

A procedure that involves leaving the water in the swimming pool over the winter, as opposed to emptying it. It includes chemically treating the stagnant water and physically protecting the swimming pool and equipment from frost.