POOL WIZARD swimming pool maintenance

Chlorine in swimming pool water

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Testing the chlorine

When planning to buy a test kit to measure the chlorine levels in your pool, it is important to remember that there a 3 aspects which can be measured:

  1. Free available chlorine (or residual chlorine) - is the amount of chlorine in the pool that can sanitise or disinfect the water and is the important measurement for us.
  2. Combined chlorine - consists of undesirable, bad-smelling, irritating compounds which form when there isn't enough free available chlorine.
  3. Total chlorine - is the total amount of chlorine in the water. It includes both free available and combined chlorine.

We are interested in how much available chlorine there is in the water - chlorine that can act on foreign substances in the water to keep the pool clean and safe for the swimmers.

Too little chlorine results in algal and bacterial growth, waterborne illnesses, cloudy water and insufficient sanitation of the water.

Too much chlorine can result in eye, nose and skin irritations. Remember, too, that the chlorine in the pool is carcinogenic and we should aim to keep its level to the minimum required for complete disinfection.

Test kits which use tablets rather than liquid reagents are preferred. The tablets are easier to use and provide more accurate results. Also make sure that the chlorine measuring tablets are "DPD" as only these can measure the free available chlorine.

Take the water sample from at least 20-30 cm below the surface and at least that far from the wall of the pool. Test the water according to the test kit's instructions.

The desirable level of available chlorine in the pool is 1.0-3.0ppm with 2.0ppm being the recommended ideal. If you are using a Pool Wizard, the ideal free chlorine level is 0.5 ppm (25% of the chlorine required in pools without a Pool Wizard).

Add chlorine according to the test results. As a rough guide, a pool needs about 600 grams of granular chlorine (2-3 cups) for each 50,000 litres of water twice a week during the hot swimming season (150 grams or 1/2-3/4 cup if using a Pool Wizard). Please note that this is only a guide, and actual chlorine requirements can only be determined by regular testing.

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