Pool Water Chemistry
Maintaining balanced pool water chemistry is one of the most important aspects of pool ownership. Correctly balanced water keeps the pool safe and comfortable for swimmers while protecting the pool shell, interior finish, plumbing, filtration equipment, heating systems, chlorinators, and other components. Whether your pool is fibreglass or concrete, routine water testing and maintenance are essential for maximising the life of your investment.
pH (7.2–7.6)
pH measures how acidic or alkaline the pool water is. It is one of the most critical water balance factors because it affects swimmer comfort, chlorine efficiency, and the protection of pool surfaces and equipment. Low pH can cause corrosion, etch concrete finishes, damage metal components, and irritate skin and eyes. High pH reduces chlorine effectiveness and can lead to cloudy water and calcium scale forming on pool surfaces and equipment.
Free Chlorine (1–3 ppm)
Free chlorine is the active sanitiser that destroys bacteria, viruses, algae, and organic contaminants. Maintaining the correct chlorine level ensures the water remains hygienic and crystal clear. Chlorine demand will increase during hot weather, after heavy pool use, following rainfall, or when organic matter such as leaves enters the pool.
Combined Chlorine (Less than 0.2 ppm)
Combined chlorine, also known as chloramines, forms when free chlorine reacts with contaminants. High chloramine levels can cause unpleasant chlorine odours, eye irritation, and reduced sanitising performance. If combined chlorine rises, the pool should be shock treated to restore effective sanitation.
Total Alkalinity (80–120 ppm)
Total alkalinity acts as a buffer for pH, helping prevent rapid fluctuations caused by rain, chemical additions, or heavy pool use. Stable alkalinity makes maintaining correct pH much easier and helps protect equipment and pool finishes.
Calcium Hardness
Fibreglass Pools: 150–250 ppm
Concrete & Pebble Pools: 200–400 ppm
Calcium hardness measures the amount of dissolved calcium in the water. Low calcium can make water aggressive, leading to corrosion of metal components and deterioration of concrete or plaster finishes. Excessively high calcium levels can result in scaling on pool surfaces, salt cells, heaters, and inside plumbing.
Cyanuric Acid (Stabiliser)
Saltwater Pools: 60–80 ppm
Chlorine Pools: 30–50 ppm
Cyanuric acid protects chlorine from being rapidly destroyed by ultraviolet (UV) sunlight. Too little stabiliser causes chlorine to disappear quickly, while excessive stabiliser can reduce chlorine's sanitising effectiveness and make algae more difficult to control.
Salt Levels
For saltwater pools, the salt concentration should remain within the chlorinator manufacturer's recommended range, typically between 4,000–6,000 ppm. Incorrect salt levels can reduce chlorine production, shorten salt cell life, and generate system error messages.
Phosphates
Phosphates are a nutrient source for algae. While they are not harmful to swimmers, elevated phosphate levels can contribute to persistent algae growth if chlorine levels are not maintained. Phosphates commonly enter the pool through rainwater, leaves, fertilisers, dust, and organic debris.