What to do if the chlorine and pH value no longer changes

09 March 2018

Usually, the chlorine and pH value changes quickly if you add a product to the swimming pool. But we often receive queries from customers who don’t see any change after adding products. The water quality can then quickly deteriorate. This says you need to act quickly.

What to do if the chlorine and pH value no longer changes

Various causes

There are various causes of this phenomenon. The first one is very simple. It may be due to the tester. If your chlorine or pH value doesn’t change when you add products, it’s a good idea to check if other water quality testers give the same or different results.

If the values do change when you test the quality with another tester, then the problem was therefore due to a defective tester.

If your 2nd tester indicates the same chlorine and pH value, the water has become too stable. This can only be due to too much cyanuric acid in the water.

Cyanuric acid in the swimming pool

Cyanuric acid in the swimming pool

Where does the cyanuric acid come from? It’s very simple, cyanuric acid is contained within the stabilised chlorine products which you add to the water. Normal chlorine tablets and chlorine granules always contain cyanuric acid, and if there is too much cyanuric acid, the water becomes too stable.

Cyanuric acid also has an important function however. Thanks to cyanuric acid, the water quality changes less quickly in sudden bad weather or heavy rainfall. At these moments, the cyanuric acid ensures that the swimming pool doesn’t turn green, or at the least, becomes less green. So the knife cuts both ways.

How can I get the cyanuric acid out of the water?

The solution against cyanuric acid is quite simple, although fairly hefty on the wallet. You need to add fresh water to the swimming pool. To do this, you will need to empty at least half of the water before adding fresh water. It’s certainly not a cheap solution.

Once the fresh water has been added, you can measure the water quality again. The pH and chlorine values will have to be adjusted in any case. The values can never be correct with all that new water. In any event, the cyanuric acid content will have reduced by half, which means that the cyanuric acid will no longer pose a problem.

As soon as the fresh water is in the swimming pool, you need to comprehensively filter the water and adjust the water quality. We recommend filtering continuously for 3 days, and measuring the water quality in the morning and evening. If necessary, you can add the required pH and chlorine product. An extra check in the afternoon might also be useful.

Afterwards, the water quality should have substantially improved. If the values are still not ideal, keep adjusting them and ensure sufficient filtration. If you want the water to be completely clear again, use HTH flocculating agent and you will see quick results.

Avoiding an excess of cyanuric acid in the swimming pool

If you’ve had problems with excessive cyanuric acid, you know you don’t want to have them again. Here are a few tips to avoid this.

The first tip is to regularly back-wash the sand filter. Back-washing removes dirt from the filter. Although quite a lot of water gets ‘lost’ in this process. You should automatically add water to the swimming pool in this case. That way, you can regularly have fresh water in the swimming pool whilst avoiding a build-up of too much cyanuric acid. Cyanuric acid doesn’t just accumulate in 1 day of course.

Furthermore, we recommend changing the water completely every 10 years. After 10 years, too much of the water in the swimming pool has already reacted with products, whereby it becomes saturated.

Avoiding an excess of cyanuric acid in the swimming pool

Bear in mind too that chlorine products also exist which do not contain cyanuric acid. You can also find liquid chlorine and HTH Granular in our webshop. Neither of these chlorine products contain cyanuric acid and are therefore ideal if you want to avoid excessive cyanuric acid. Caution: the pH and chlorine values will change more quickly with these products.

A final tip is to test the water quality several times per week, and ensure sufficient filtration. By regularly testing, you can see the water quality change. That way, you can intervene more quickly and your swimming pool will remain clear.

Liquid chlorine

Liquid chlorine 20L

HTH Granular 10 kg

HTH Granular 10 kg