The alkalinity is helpful in the swimming pool, but the level must not be too high. When the alkalinity is too high, it is more difficult to modify the water chemistry. We will see here how to lower the alkalinity of the pool. Decreasing alkalinity often goes hand in hand with pool pH.

What is the alkalinity of the swimming pool?

Alkalinity represents the amount of carbonates, bicarbonates, and hydroxides in the water. The alkalinity of the water is measured by making a Complete Alkalimetric Title (CAT). Chemically, CAT = HCO3– + CO3= + OH–.

Why is this important? Alkalinity in a pool is important because it considerably impacts pH variations. You may have trouble stabilizing the pH, and this will often be because of an alkalinity problem. It is the underlying cause of other issues. Alkalinity is often presented as the “buffering” power of the pH because this property interests us.

What is a too-high alkinity?

The ideal alkalinity for a swimming pool is between 80 mg/L and 120 mg/L. Above 120mg/L is too high alkalinity.

Risk and consequence of too high a TAC in the pool

For human health, there is no problem bathing in water with a too-high alkalinity. No worries on this point.

Too-high alkalinity in the pool will make water treatment more complicated. We have spoken of the alkalinity as representing the buffering capacity of water on the pH. When this buffering capacity is too high, more chemicals will be needed to lower the alkalinity.

Too-high alkalinity often comes with an increasing pH.

How to measure the alkalinity of the swimming pool?

Complete Alkalmetric Title (CAT) is a colorimetric analysis. We will take a water sample to make it react with another chemical product. The resulting color represents the CAT level.

The best-known and the most used in the field of the swimming pool are the strips and the tablets.

There is no electronic TAC tester. Technology does not exist.

Making precise readings for businesses with a swimming pool for collective use, such as campsites or guest houses, is necessary. For these cases, a photometer can be used. The photometer works the same way as strips and tablets. Instead of interpreting the color with an eye, it is a sensor that will convert the color obtained into a precise value. It’s very reliable.

There is only one way to measure alkalinity: by reacting water with a chemical. There are then 2 ways to interpret the result: with the naked eye or with an electronic sensor.

Why does the TAC vary?

Good news with alkalinity: it varies relatively little over time. Unlike pH or Chlorine, alkalinity does not necessarily require analysis every week for a private pool. We will therefore have less need to lower the alkalinity of the pool during the year.

Alkalinity varies for the same reasons as other water chemistry parameters. Any new element in the water modifies the chemical parameters: the leaves, the swimmers’ sweat, etc.

Products to lower the TAC

There is no magic product to lower alkalinity. All products will also impact pH.

To lower the TAC, you can therefore use one of the 3 products that lower the pH:

• hydrochloric acid
• sodium bisulfate (or sodium hydrogen sulfate)
• sulfuric acid

You can find products called “Tac Minus” to lower alkalinity. They usually contain one of these 3 products. Powdered products often use sodium bisulfate.

Find all the details on these products on our page dedicated to lowering the pH.