The Importance of pH in Pools and Hot Tubs

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Measuring the pH of your hot tub water tells you how acidic (low pH) or alkaline (high pH) your hot tub water is on a scale of 0 to 14. The reason you should try to maintain your hot tub or swimming pool water between pH 7 and pH 7.4 is partly down to bather comfort, but mostly down to sanitiser efficiency. When chlorine sanitiser* is added to your swimming pool or hot tub it combines with water to form a mixture of the sanitisers, hypochlorous acid and hypochlorite. As the blue lines in the graph on the right shows, the ratio of chlorine available to sanitise in the form of hypochlorous acid to hypochlorite depends on the pH of your hot tub or swimming pool water. Hypochlorous acid is 80 to 100 times more effective as a sanitiser than hypochlorite, so you really want to have more hypochlorous acid present than hypochlorite. 

The lower the pH, the more efficient the chlorine is at sanitising the water. But you don’t want your water to go below pH 7 because that will start affecting the overall balance of the water, which can  lead to skin and eye irritation and can even cause damage to the pool or hot tub. Above pH 7.5 sanitiser’s (chlorine or bromine) bactericidal efficiency drops off massively. The solid red line on the graph shows the effect of pH on the relative available chlorine and hence, available bactericidal activity.



Graph showing chlorine effectiveness with changing pH

Used in combination, Pennosan® Natural Clarifiers boost sanitiser performance by removing organic TDS (Total Dissolved Solids). Pennosan Natural Pool and Natural Spa Clarifiers also work best between pH 7 and pH 7.4 – the ideal pH range for your pool or hot tub.


*In the absence of cyanuric acid.

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