Pool Terminology

Are you a new owner of a swimming pool or spa? Confused with the terminology used in swimming pool or spa water treament?  Explore the list below to find out more.


Acid - a chemical which provides hydrogen ions (H+) to lower the pH and the total alkalinity of water.


Acidity - any measure below pH 7 on the pH scale is considered to be acidic.


Algae - microscopic plants that grow when water and light are present. Algae can form when chlorine levels in the pool become too low, especially in bright sunlight and high temperature conditions. It's mainly seen in pools in its green form but can also be red/black/mustard in colour.


Algicide - a chemical which can be used to combat and prevent the growth of algae in the pool.


Alkali - Any measure above pH 7 on the pH scale is considered to be alkali.


Available Chlorine - this is the amount of chlorine released when dosed into a pool. It is measured in parts per million and mg/l.


Backwash - to reverse the flow of water back through the filter.


Bacteria - Microscopic organisms which can cause bather discomfort, illness or disease.


Balanced Water - indicates the water contains just the right amount of calcium hardness, total alkalinity and pH so as to prevent scale forming or corrosive tendencies.


Bather load - the number of people using a pool at any given time.


Bromine - an alternative pool sanitiser to chlorine.


Calcium Hardness - is a measure of the amount of dissolved calcium and magnesium in the pool water. If there is a calcium deposit on the bottom or the sides of your pool, it is no longer dissolved. The recommended range is 75-150mg/l.


Calcium Hypochlorite - Chlorine based sanitiser that is stabiliser free. Sometimes referred to as Cal Hypo.


Chlorine - a commonly used disinfectant for water.


Chlorine Demand - the amount of chlorine required to destroy bacteria, algae and other water contaminants which must be met before a free chlorine residual can be established.


Chlorine lock - this describes the situation when chlorine becomes less effective due to the pool being over stabilised, i.e. too much cyanuric acid.


Chloramines - formed when free chlorine comes into conatct with nitrogen contained in waste products such as perspiration, soap and urine. Also referred to as combined chlorine. High levles can give off a very strong, unpleasant smell of chlorine and cause irritation to the eyes and skin.


Clarifier - can clear cloudy water by pulling the small suspended particles together to make larger particles which can then be filtered or vacuumed out.


Combined chlorine - Total Chlorine minus Free Chlorine


Copper - a metal which may be present in water that may result in coloured water (blue-green) or coloured stains from precipitation.


Corrosion - is the chemical deterioration of metal, plaster or other materials caused by improperly balanced water.


Cyanuric Acid - used as a stabiliser it is the chemical that prevents loss of chlorine to sunlight. If present in excess however, it may inhibit chlorine activity.


Di-Chlor - A type of chlorine-based sanitizer which is self-stabilized (contains cyanuric acid), that is used to kill bacteria, control algae and oxidize contaminants.


Dry Acid - A commonly used name for pH/alkalinity reducer (sodium bisulphate)


Free Chlorine - this is the same as available chlorine


Iron - a metal which may be present in water that may result in coloured water (rusty, yellow-brown) or coloured stains from precipitation.


Oxidation - the process of chemically "burning up" contaminants by causing it to combine with the Free Available Chlorine.


pH - a measure of how acidic or alkali the water is. The scale runs from 0 - extremely acidic, to 14 - extremely alkali. A low pH in a pool can cause skin irritation and corrosion to pool equipment. A high pH can result in cloudy water, encourage scale formation and reduce the effectiveness of the sanitiser. The ideal range for swimming pool water is between 7.2 and 7.6


Phosphates - chemical compounds containing phosphorus and oxygen. They can enter the swimming pool via mains top-up water, urine, garden run-off following heavy rain and even airborne dust. They are essential nutrients needed to support life and are therefore a major nutrient source for algae growth in swimming pool water. Removing them will dramatically reduce the potential for algae growth.


pH neutral - is pH 7


PPM - parts per million is the same as milligrams per litre (mg/l). It is used to measure very dilute concentrations of substances.


Required chlorine - the amount of chlorine needed in your pools to remove bacteria, algae and other pollutants.


Scale - the precipitate formed when excess calcium carbonate is present in the water due to high pH and Total Alkalinity.


Shock treatment - dosing your pool with an unstabilised chlorine, but at a much larger rate than a normal dose. The aim of this is to remove all the pollutants that are affecting the quality of your water.


Skimmer - a basket to hold tablets which fits into the poolside. Water skims over it to dissolve the tablets.


Soda Ash - A commonly used name for pH increaser


Soft water - water prone to producing lime scale deposits.


Stabilised Chlorine - Chlorine which contains cyanuric acid. This prevents the loss of chlorine to sunlight.


Stabiliser Free Chlorine - Chlorine which is free of cyanuric acid.


Total Alkalinity - is the measurement of the total alkaline substances dissolved in the water. High total alkalinity makes the pH more difficult to adjust. Low total alkalinity could cause the pH to fluctuate irregularly. The ideal range is 80 - 150mg/l


Total Alkalinity - the sum of bicarbonates, carbonates, and hydroxides in water, which act to buffer the water against sudden changes in pH. Improper Total Alkalinity levels may result in difficulty adjusting pH.


Total chlorine - a measurement of free chlorine and combined chlorine in pool water.


TDS - the abbreviation for Total Dissolved Solids. This is a measure of all the solids dissolved in the water. If your TDS level is too high - usually high salt residues from pool chemicals - your pool may appear darker, have a salty taste and ultimately corrosion will occur.


Water balancing - ensuring your pool water has the required levels of ph, total alkalinity, calcium hardness and dissolved solids, through regular testing and maintenance.