Alkalinity is one of the most critical chemical parameters of swimming pool water. It is often ignored when you start, but sooner or later, you have to learn to master it. We will see the consequence of too-low alkalinity in the pool and how to increase it. There’s only one way to measure pool alkalinity and only one product to raise it. Explanations.
What is the alkalinity, the TAC, 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, TAC = 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 low TAC?
The ideal TAC for a swimming pool is between 80 mg/L and 120 mg/L. Below 80 mg/L is too low alkalinity. When the alkalinity is too low in the pool, the alkalinity must be increased to avoid risks.
Risk and consequence of too low a TAC in the pool
For human health, there is no problem bathing in water with a low alkalinity. No worries on this point.
The main risk is the instability of the pH and the consequences thereof. Water has little or no buffering capacity, so the pH can vary very quickly.
Everything that comes into contact with water will modify the pH: bathers, rainwater, dust. Without buffering capacity, the pH will vary a lot in significant proportions. We can then lose several pH points quickly and end up with aggressive water for the skin, algae development, and dangerous water.
How to measure the TAC, alkalinity, of the swimming pool?
Complete Alkalimetric Title (CAT) is a colorimetric test. 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 raise the alkalinity
Alkalinity is intimately linked with pH. It is complicated to change one without changing the other.
The best way to raise the TAC when it is too low in the pool is to use sodium bicarbonate (also called baking soda).
Baking soda is often sold in powder form under the name “Alkalinity Increaser” in stores. You can check the composition on the packaging of each product.
Alkalinity Increaser. The baking soda will affect both the Tac and the pH. The two parameters are closely related, and changing one without touching the other is impossible. The baking soda will increase the alkalinity and the pH in the pool. However, the bicarbonate will increase the alkalinity faster than the pH.
Dosage. The notices generally indicate a quantity of 18 g/m³ to raise the alkalinity by 10mg/L.
Avoid big treatments. Avoid putting more than 50g/m³ of product in the pool. For example, for a 50m³ pool, you should avoid adding more than 2.5kg at once. It will be too big a shock for the water, and there is a big risk that the water will become cloudy. In addition, we always recommend going in small doses because the water balance of a swimming pool is very complex. Add only 50% of the required quantity and wait 24 hours to see the evolution of the water quality in the pool.
Increase alkalinity without increasing pH
Unfortunately, there is no solution to increase the alkalinity without raising the pH. The two work together. If your pH is ok, then you have to lower it to around 6.9 with one of the products to lower the pH, wait a few days, then raise the pH and the TAC with bicarbonate.