Acid. A chemical which lowers pH when added to pool water.
Active Bromine. Bromine which is readily available for killing bacteria and algae. It is measured by DPD No.1 test tablet and includes free bromine and some bromamines.
Algae. Microscopic aquatic plant life which grows on pool surfaces or floats freely in the water. Green, blue-green (commonly called black) and brown, reddish brown, and yellow organisms known as "mustard algae" are the strains most commonly found in swimming pools.
Algicide. A chemical compound used to kill or inhibit the growth of algae.
Alkali. A term applied to soluble carbonates and hydroxides. (Refer to base)
Alum. Short for Aluminium Sulphate. See flocculant.
Amperometric. This is a method of determining chlorine levels often used in automatic controllers incorporating either platinum/platinum or platinum/copper electrodes.
Amperostatic (Potentiostatic). A method of measuring chlorine residuals used in automatic controllers using platinum/gold electrodes.
Aquabrome. Trade name for dry organic compound 1-Bromo-3-chloro-5,5-Dimethyldantoin, a bromine based swimming pool disinfectant.
Bacteria. Microscopic organisms, some of which can cause disease. They are brought into the swimming pool by bathers, wind, dust, rain and surface drainage.
BackWash. Method of cleaning the filter media of a sand filter by reversing the flow of water and running it to drain.
Balanced Water. Water which has been assessed to be chemically in balance so it is neither corrosive nor scale forming.
Base. A chemical which raises the pH when added to swimming pool water. Sodium carbonate (soda ash) and sodium hydroxide (caustic soda) are examples of bases.
Bather Load. The number of individuals using a pool in a 24 hour period and the pool's principal source of bacterial and organic contamination.
Breakpoint Chlorination. Method of chlorination in common use, involving the addition or chlorine to pool water to a point where most of the organic matter is oxidised allowing the existence of a free chlorine residual.
Bromamines. A number of bromine-ammonia compounds exhibiting sanitising properties similar to hypobromous acid (HOBr). Unlike their chlorine counterparts (chloramines), bromamines do not leave a pungent odour nor do they give rise to eye and mucous membrane irritation. Monobromamine is an effective disinfectant.
Brominator. The dispensing device for feeding Aquabrome into a pool's recirculation system.
Bromine. A disinfectant added to swimming pool water to destroy and inhibit bacterial viral and algal growth in addition to oxidising (burning out) unwanted organic matter. Elemental bromine is a very corrosive reddish-brown liquid. It is little used in UK public pools.
Bromine Demand. The amount[ of active bromine required to destroy and oxidise bacteria, algae and other organic compounds. When the demand is satisfied and active bromine can be measured in the water, the water is considered sanitised and safe for use.
Bromine Residual. See 'Residual Bromine'.
1-Bromo-3-Chloro-5,5-Dimethylhydantoin. An organic compound containing 66.2% available bromine and 29.4% available chlorine bound to a carrier dimethylhydantoin. It is available as a proprietary pool disinfectant trade name Aquabrome.
Buffer. A chemical which when dissolved in swimming pool water will resist pH change. Sodium bicarbonate is an example of this type of chemical.
Calcium Hardness. The quantity of calcium dissolved in water. The minimum level suggested is 250 mg/l, although the preferred level is 500 mg/l. High levels can promote scale and cloudy water if the water is incorrectly balanced. Low levels can lead to corrosion and grout loss.
Cal. Hypo. The usual way of referring to calcium hypochlorite, a granular calcium based chlorine donor with typically 65% available chlorine.
Calorifier Another name for a heat exchanger used to indirectly heat pool water.
Carbon Dioxide (CO2) A gas used for pH correction. When introduced into pool water it forms carbonic acid and so lowers pH. It is suggested that it is not cost effective to use carbon dioxide in pools where the make up water has an Alkalinity of 150 mg/l + as CaCO3, or a Calcium Hardness in excess of 300 mg/l as CaCO3.
Chloramine. When nitrogen compounds are introduced to pool water as waste material from bather's bodies they are oxidised by chlorine, at this time chloramines may be formed. Chloramines exist as either monochloramine, dichloramine, or trlchloramine. Trichloramine is a particular irritant and has a pungent smell. Chloramines have little disinfecting powers.
Chlorine. A disinfectant added to swimming pool water to destroy or inhibit bacterial and algal growth in addition to oxidising unwanted organic matter. Available in the inorganic form as a gas, liquid or solid and in the organic form of chlorinated cyanurates.
Chlorine Demand. The amount of chlorine required to destroy bacteria, algae and/or other organic matter in water before an active chlorine residual can be achieved.
Combined Chlorine. The amount of chlorine and ammonia combined to form chloramines. Measured by the difference between the No.1 and No.3 DPD tests.
Combined Bromine. Bromine which has reacted with nitrogen to form Bromamines.
Corrosion. The etching of metal from metal surfaces in a destructive manner by chemical or electrochemical attack. Corrosion can be caused by low pH, low total alkalinity, low calcium hardness or a combination of all three. High TDS levels are also corrosive.
Cyanuric Acid. A stabiliser added to pool water to screen active chlorine against loss due to the ultra violet rays of the sun.
Disinfect. To kill or inhibit the growth of harmful bacteria and virus in swimming pool water.
DI-chlor. Short for Sodium Dichlorolsocyanurate Dihydrate, a chlorinated Isocyanurate with 55% available chlorine.
DPD. Short for N.N.Diethyl-p-PhenyleneDiamine Sulphate. A chemical reagent which reacts with active bromine or chlorine and turns the water sample pink. The darker the pink, the higher the bromine or chlorine content. Test sets using DPD are preferred over other methods. OTO should not be used. DPD No.1 measures active bromine or free chlorine. DPD No. 3 measures total halogen when used with DPD No. 1.
Dry Acid. Sodium Bisulphate or Sodium Hydrogen Sulphate used to reduce pool water pH and alkalinity.
Elemental Bromine. A heavy reddish-brown liquid (at room temperature). Like chlorine gas it is highly toxic and must be handled with the greatest of care.
Flocculant. Material used to aid filtration allowing the removal of small particles.
Free Active, Free Available or Free Residual Chlorine. Chlorine which has not combined with pollution, i.e. Hypochlorous Acid (HOCL) a very powerful disinfectant. Tested for with DPD No.1 test tablets.
Free Bromine. Bromine present in the form of Hypobromous Acid (HOBr).
Halogen. A chemical family which includes chlorine and bromine.
Hydrochloric Acid (HCL). An acid used to lower pool water pH and alkalinity. Supplied in liquid form and must be handled with great care.
Hypobromous Acid (HOBr). One of the active species present in bromine treated pool water. In addition to being an effective bactericide and oxidiser, it is also noted for its viricidal properties.
Hypochlorous Acid (HOCL) . The active species present In chlorinated pool water. It is a very powerful bactericide and oxidiser.
Injection Points. Usually refers to the points at which chemicals are introduced into the pool circulating system. Normally hypochlorite is dosed pre-filter and acid is dosed post calorifier. Flocculant is obviously dosed pre-filter.
Liquid Chlorine. Often used to describe sodium hypochlorite or other chlorinated solutions. Strictly speaking liquid chlorine is liquified chlorine gas.
Organic Wastes. Nitrogen and ammonia bearing compounds such as urine, saliva, perspiration, body oils and sun tan lotions that are continually being introduced into pool water by bathers. Most organic wastes will not filter out and therefore must be chemically removed (oxidised).
ORP. Also known as Redox. Oxidation Reduction Potential is an index of sanitizer activity. It measures the activity of the sanitizer rather than the quantity.
OTO. o-Tolidine, a chemical reagent formerly used in pool water test kits for measuring chlorine residuals. The compound is now considered a health risk and should no longer be used.
Ozone (O3). A powerful bactericide gas used as a pool water disinfectant.
pH. The pH scale is the negative logarithm of the hydrogen ion content of pool water. In normal swimming pool terms the pH is a measurement of the relative acidity or basicity (alkalinity). The scale runs from 0 (very acidic) to 14 (very basic), with neutral being approx pH7.
Phenol Red. A chemical reagent used in the measurement of pH. Phenol Red needs to be 'inhibited' so as not to be affected by the bromine or chlorine in the water sample. When using phenol red test tablets this inhibition is already taken care of .
PPM. Stands for parts per million, the usual units used to measure chlorine residuals etc. It is the same as milligrams per litre (mg/l).
Progressive Dilution Theory. This says that 66% of the pollution in pool water is removed each turn-over. If say 100 children entered a pool for 1 Hour then the pool was left empty, after one turn-over 66% of the pollution would be removed, after a further turn-over 66% of the remaining 34% would be removed leaving approximately 10%. A further turn-over would remove 66% of this 10% and so on.
Reagent. Chemical used to test concentrations of specific compounds in pool water .
Redox. see ORP
Residual. The amount of a compound existing in pool water, usually expressed as parts per million (ppm) or millgrammes per litre (mg/l).
Residual Chlorine. The chlorine residual remaining in pool water in a free state after the chlorine demand has been satisfied. The normal minimum free chlorine residual is 1.0 - 1.5 ppm (mg/l).
Residual Bromine. The bromine remaining in an active state after the pool water's bromine demand has been satisfied. The recommended bromine residuals are 1.0 - 3.0 ppm (mg/l) for residential pools and 4.0 - 6.0 ppm (mg/l) for public pools.
Sanitizer. A disinfectant.
Saturation Index. Usually refers to the Langeller method of water balance test.
Scale. The mineral deposit or precipitate, on floors walls, metal piping, filter systems etc., usually calcium carbonate. It can become unsightly and interfere with pool operation. Under controlled conditions it can be used to aid corrosion inhibition.
Sequester or Chelate. Specially formulated chemicals used to hold metals, e.g. iron, copper, or calcium in solution to prevent scaling or staining.
Shock. The process of introducing significant quantities of a sanitizer to the pool to bring about the chemical destruction (oxidation) of excess organic matter or high combined chlorine levels.
Sodium Bicarbonate (NaHCO3) Also known as baking soda. Used to raise the alkalinity of pool water.
Sodium Bisulphate (NaHSO4). Also known as dry acid used to reduce the pH (by trickle feeding) and alkalinity (by dumping) of pool water.
Sodium Carbonate (Na2CO3). Also known as soda ash. Used to increase the pH level of pool water.
Sodium Thiosulphate (Na2S2O35H2O). Used to neutralise chlorine in pool water. Should be used with great care.
Soften. In relation to pool water it is the removal of water hardness. The softening of swimming pool water is not recommended.
Stabiliser. see Cyanuric acid.
Total Alkalinity. A measurement of the total amount of alkaline (base) chemicals in the pool water.
Total Bromine/Chlorine. A measurement of all the active and inactive bromine or chlorine compounds in pool water as measured by DPD No. 4 (DPD No.1 + DPD No.3) test tablets.
Total Dissolved Solids.(TDS). Collective name for salts dissolved in the pool water, derived from the chemicals being used. High TDS levels can cause sanitizer inefficiency, cloudy water and corrosion. Recommended maximum level 1500 ppm (mg/l).
Trichlorinator. A device for feeding Trichloroisocyanuric Acid tablets into the pool circulating system.
Tri- Tabs. Trade name for Trichloroisocyanuric Acid Tablets a chlorinated isocyanurate with 90% available chlorine. Tablet size is 300 gms. Other tablet sizes available are 14 gms (mini-tabs) and 200 gms (maxi-tabs).
Turn-Over. The time taken to theoretically circulate the total volume of pool water through the plant once. Determined by the capacity of the pool circulating pump.
Virus. Submicroscopic infective agents capable of growth and multiplication only in living cells and which can cause various diseases in man or other animals.


Kilograms x 2.205 = Pounds Imperial Gallons x 4.54 = Litres
Pounds x 0.454 = Kilograms Litres x 0.22 =Imperial Gallons
Ounces x 28.35 =Grams Imperial Gallons x 0.0045 = Cubic Metres
Grams x 0.035 =Ounces Cubic Metres x 220 = Imperial Gallons
Metres x 3.279 = Feet Imperial Gallons x 0.833 = U.S. Gallons
Feet x 0.305 = Metres U.S. Gallons x 1.201 = Imperial Gallons
Prepared By : Howard Gosling BSc. PrimeMix Ltd.
  Mick Lipscombe M.lnst.B.R.M. (Dip) PrimeMix Ltd.
With Contributions From : Gerry Hawksby F.Inst.B.R.M. I.B.R.M. Southern Training Officer
  Geoff Shute LRSC MIWEM The Tintometer Ltd.
  Alan Jones M.lnst.B.R.M.(Dip) Olin (U.K.) Ltd.