Your pool's pH can gradually increase due to both the chemicals used to sanitise the water and environmental factors. While a slow rise in pH is normal, allowing it to remain too high can reduce chlorine effectiveness and lead to other water quality problems.

Some of the most common causes of high pH include:

• Salt chlorinators

If your pool uses a salt chlorinator, it's normal for the pH to slowly drift upwards over time. During the electrolysis process, the chlorinator cell creates chlorine, but it also produces a highly alkaline environment around the cell, with a localised pH that can exceed 12. Although this high pH is diluted as the water circulates, it gradually causes the overall pool pH to rise.

• Aeration and water movement

Strong winds, waterfalls, spa spillways, fountains and even swimmers splashing the water can all increase aeration. As the water is aerated, carbon dioxide (CO₂) escapes into the atmosphere.

Carbon dioxide naturally helps keep the water slightly acidic. As CO₂ is lost, the water becomes more alkaline, causing the pH to rise.

• High-pH chemicals

Some pool chemicals, including certain alkalinity and calcium products, can also increase the pH if they are not added in the correct amounts.

Why Is It Important to Keep Your pH Between 7.2 and 7.6?

Maintaining your pool's pH between 7.2 and 7.6 is one of the most important aspects of water chemistry.

1. Chlorine works much better

The effectiveness of chlorine decreases as the pH rises.

• At around pH 7.2, chlorine is at its most effective.

• By pH 7.6, chlorine has already lost around 50% of its sanitising power.

• Above pH 8.0, chlorine may be operating at only around 20% effectiveness.

This means that even if your chlorine test shows an acceptable reading, the chlorine may not be able to effectively kill algae and bacteria if the pH is too high. As a result, your pool becomes much more likely to turn green.

2. Better comfort for swimmers

Keeping the pH within the recommended range helps minimise eye and skin irritation, making the water more comfortable for everyone using the pool.

3. Protects your pool equipment

High pH encourages calcium scale to form on pool surfaces, inside pipework, and on salt chlorinator cells and reduce equipment efficiency.

On the other end, low pH (below 7.2) can cause several problems for both swimmers and your pool:

• For swimmers: Low pH can cause eye irritation, skin irritation, itchy skin.

• For your pool: Acidic water is corrosive. It can damage metal components such as ladders, light fittings, heaters, and salt chlorinator cells. It can also etch plaster and concrete surfaces and shorten the lifespan of pool equipment.