Disinfectants
A sufficient level of active disinfecting chemicals must be continually present in the water to destroy all harmful microorganisms.
Free chlorine can be measured on a test kit using DPD No. 1 tablet.
Combined chlorine can be measured by a test kit using a DPD No. 3 tablet.
Ask your pool technician how to sample for free and combined chlorine. There should always be less combined chlorine than free chlorine in a well-managed pool.
Unstabilised (indoor) pools and spas – chlorine
It is important to maintain a free chlorine level of at least:
- 1 milligram per litre for water temperatures below 26 °C
- 2 milligrams per litre for water temperatures above 26 °C.
Stabilisers should not be used in a spa or indoor pool.
Stabilised (outdoor) pools – chlorine
It is important to maintain, at all times, a free chlorine level of at least:
- 2 milligrams per litre for water temperatures below 26 °C
- 3 milligrams per litre for water temperatures above 26 °C.
Other chemicals
Stabiliser (isocyanuric acid)
Isocyanuric acid should be maintained at a level between 30 and 50 milligrams per litre.
Stabiliser is recommended in outdoor pools that use chlorine.
Acidity or pH level
The pH reading is a measure of how acidic (low pH, below 7) or alkaline (high pH, over 7) the water is, with a pH reading of 7.0 being neutral.
The effectiveness of the disinfecting chemicals depends on the pH of the water. Chlorine works best when the pH reading is between 7.2 and 7.8, with a reading of 7.5 ideal for bathers.
Factors that can affect your pool's pH level include:
- heavy rain
- the number of swimmers in the pool
- use of chemicals.
Remember to regularly check the pH level daily.
Regular water testing is important
Check the chemical levels in your pool or spa water at least once a day.
The most important chemical levels are the:
- free chlorine or free bromine levels
- pH levels
Free chlorine and free bromine levels are generally measured using DPD 1 reagents.
pH levels are measured using Phenol Red reagents. Both DPD1 and Phenol Red are available in a tablet form from pool equipment stockists or shops.
If you use stabiliser (isocyanuric acid) in your pool or spa you should also check the level of this chemical at least once a day.
On hot days, test the water in swimming pools before your first swim and at least once again during the day.
Heated spa pools should be tested at least twice a day whenever in use.
If the results show chemical levels are too high or too low, you will need to take corrective action.
Never add chemicals while people are in the water. Allow at least 30 minutes for chemicals to dissolve into the water before anyone enters the water.
For advice on the types of test kits available contact your trained local pool and spa technician.
Manual or automatic dosing?
Chemicals can be added to water manually or via an automatic dosing system.
Automatic systems are simpler for maintaining water quality because they test the water chemistry and add the required amount of chemicals.
For busy people the use of an automatic chlorine dosing system or salt pool generated by electrolysis is a good idea. For home owners with more time, a hand dosed system can be used. Automatic systems can be programmed to operate when you are absent from the home.