All about pH on pool / spa water

pH plays a crucial role in maintaining healthy, balanced water in your pool or spa. The pH varies according to a number of factors, so it's important to check it regularly. In this article, we explain in detail what the pH is, how to measure it and what to do if it's too high or too low.

Definition of pH

The pH is a measure of the acidity of water, indicating the concentration of hydrogen ions. The pH scale ranges from 0 to 14. A value of 7 is considered neutral, and water below 7 is acidic. Above 7, it is alkaline.

The importance of a balanced pH

The pH balance in your pool or spa is of paramount importance because of its impact on pool disinfection. The pH balance also influences the disinfectant's ability to effectively kill bacteria and harmful organisms in the water. The correct pH ensures that the disinfectant can work optimally and eliminate unwanted contaminants. This helps maintain safe, healthy water for bathers, reducing the risk of infection or illness.

The recommended pH differs according to your disinfection method:

• For chlorine disinfection, the ideal pH is between 6.9 and 7.4

• For bromine disinfection, the ideal pH is between 7.5 and 7.8


Another aspect to consider is the effectiveness of complementary products such as algaecides or flocculants, which help to prevent algae growth and maintain clear water. These products work best in an environment with a balanced pH, maximising their beneficial effects.


The risks of an unbalanced pH

The outside temperature, the use of the pool (frequency and number of bathers) and the dosage of treatment products all affect the pH of the water.

An incorrect pH can compromise the effectiveness of disinfectant products such as chlorine or bromine. It can also irritate bathers' skin and eyes, change the colour of the water and lead to the growth of algae.

  • A pH that is too high reduces the effectiveness of the chlorine, requiring more product to keep the water clean and bacteria-free.
  • A pH that is too low can lead to over-chlorination and make the water uncomfortable for bathers.

Measuring pH

To measure the pH of your pool or spa, you can use test strips, for example. If you choose this measurement system, we recommend that you test the pH regularly, at least once or twice a week.

You can also use a connected water analyser like ICO. This connected water monitor lets you measure a wide range of parameters in your pond, including temperature, TDS, pH and ORP-redox. With this type of tester, you can let yourself be guided. Measurements of your pH and other parameters are sent to you at regular intervals, making it easier to manage your water parameters.

What should I do if my pH is too high?

Reasons for and consequences of a high pH

A high pH can have various causes:

  • mains water with a high pH
  • the frequency of swimming
  • the presence of urine in the water
  • the addition of pH+.

A high pH can have harmful consequences for your pool. For example, it is responsible for cloudy water, incrustations on the walls and a lack of effectiveness of disinfectant products. A high pH can also irritate bathers' eyes.

Comment baisser un pH trop haut?

If the pH of your spa or pool is too high, here's what you can do to lower it:

• You will need to add pH- containing an acid product, such as hydrochloric acid or sulphuric acid.

• Be sure to follow the manufacturer's instructions carefully regarding the quantities to be used. Wear protective equipment such as gloves and safety goggles when handling chemicals.

• Dissolve the acidic chemical in a bucket of pool water before adding it to the water. This will prevent any damage to spa or pool surfaces.

• Add the acidic chemical in small quantities, mixing the water well after each addition, then wait a few hours or according to the manufacturer's instructions to allow the pH to stabilise.

• After the waiting time, test the pH again to see if it is within the target range. If the pH is still too high, repeat the process, adding smaller quantities of the acidic chemical until the desired value is reached.

• Once the pH is within the ideal range, it is essential to monitor the pH of your spa or pool regularly to ensure that it remains balanced.

What should I do if my pH is too low?

A low pH can be caused by a number of factors:

  • relatively acid rain
  • ambient pollution
  • the pH of the mains water
  • the addition of pH-

A low pH can also have harmful consequences for bathing quality and equipment. It can lead to corrosion of equipment, deterioration of pool walls, excessive use of disinfectant and irritation of bathers' eyes and skin.

That's why it's so important to keep the pH of your pond under control.

How can I raise a pH level that's too low?


If the pH is too low (acidic):

• Add pH+, which contains an alkalinising agent such as bicarbonate of soda or sodium carbonate. Follow the manufacturer's instructions to determine the appropriate amount to add according to the size of your spa or pool.

• Dissolve the chemical in a bucket of pool water before adding it to the water. This will prevent damage to spa or pool surfaces. Make sure you mix the water well to ensure even distribution of the chemical.

• After adding the chemical, wait at least 6 hours, then re-test the pH to make sure it is within the ideal range.

• If the pH is still not within the target range, you can repeat the process by adding smaller quantities of the alkalising agent, testing regularly to avoid exceeding the desired pH.

Caution: add the pH+ gradually so as not to unbalance the other parameters of your pool.

As always, safety is paramount when handling chemicals. If you have any doubts or are having difficulty adjusting the pH of your spa or pool, don't hesitate to consult a pool and spa maintenance professional for advice specific to your situation.

Be sure to follow the manufacturer's instructions carefully regarding the quantities to be used and wear protective equipment such as gloves and safety goggles when handling chemicals.

The pH does not change after adding pH - or pH+? 

If the pH of the water does not change after the addition of pH - or +, this may mean that your water is not buffered. The alkalinity level is therefore too high.

  • For your pool: Add liquid pH- then activate continuous filtration to lower the TAC . This will change the pH.
  • For your spa: activate the jets continuously to release the minerals in the form of gas.

You can watch our video explaining pH.

What is pH? A chemist tells you everything in video to better control the water of your pool or spa.