The pH of your swimming pool water will have a significant impact on the efficiency of your chlorine sanitiser such as OPC Chlorine Shock Granules, OPC Liquid Chlorine (Sodium Hypochlorite) 14/15%, OPC Stabilised Chlorine Granules and OPC Large Chlorine Tablets, if the pH is too high (above 7.5) the efficiency of chlorine starts to drop. With a pH reading of 7.8 and above the chlorine is starting to work very slowly and can lead to cloudy / dull water conditions, if the water has turned green it can be difficult to restore clarity.

Another impact of long-term high pH reading can be the formation of scale on the walls and floors of the swimming pool and internal pipework including the plant such as the circulation pump and filter. This situation is further impacted when the water conditions are known to include hard water (scale forming) the quickest method of establishing if you live in a hard water area is look at the inside of your kettle to see if there is a build-up of limescale. If this is the case ensure the pH of your water is no higher than 7.5

However, if the pH is too low water conditions can become unpleasant for bathers and could cause damage to the fabric of the swimming pool so getting the correct pH balance is vital.

As a rough guide the following offers a guide to the effectiveness of chlorine at 3 key pH readings

  • pH 7.0                                   Chlorine efficiency is around 70% (very high)
  • pH 7.5                                   Chlorine efficiency is around 45% (normal operating conditions)
  • pH 8.0                                   Chlorine efficiency is around 20% (very low – chlorine not working well)

As you can see from the above guide the correct pH balance is vital so that you achieve the most from the chlorine sanitiser.

To achieve the correct pH balance is straightforward, regularly test the water (we recommend daily) with a Pooltester and follow these easy steps.



  • The ideal pH balance should be 7.2 – 7.5

Adopting this simple and straightforward regime will ensure you achieve the maximum benefit from your swimming pool or hot tub this season.

*Use biocides safely.  Always read the label and product information before use.