This is the third post in my chemical series. Today I will discuss pH, what it is and how to control it.
pH is a number representing the acidity or alkalinity of your water. The preferred range for a pool is between 7.2 – 7.6. The lower the number, the more acidic the water is. We can lower the pH by adding an acid to the water and we can raise the pH by adding a base.
I have to discuss total alkalinity here briefly because of its effect on pH. We adjust alkalinity by adding sodium bicarbonate (baking soda) to increase it and muriatic acid to decrease it. These chemicals also affect the pH and I will get into that a little more in my next post. The important thing to understand about alkalinity at the moment is that it works as a buffer for the pH. In other words, if the alkalinity is at 0 and we try to lower the pH by adding a very small amount of muriatic acid to the water, the pH will descend well below 7.0. Again, with an alkalinity of 0, the same is true when we add a little soda ash. The pH will ascend way above 8.0. This is why the alkalinity is very important to controlling pH. It allows us to control the pH with precision.
To adjust pH down, we can add either a dry acid or muriatic acid. This may also lower the alkalinity, so it is important to retest the water several hours later. My advice on adjusting the pH up is to first determine if the alkalinity is low as well. If the alkalinity is low then raise it first with sodium bicarbonate or baking soda. This will also raise the pH and only then should you add soda ash if needed to raise the pH any more. Soda ash has a tendency to cloud the water, so I would not recommend it unless necessary.
You should check the pH often (once or twice a week). It is very important to your equipment, the pool surface, and yourself. A pool with a high pH is also more likely to grow algae. A low pH is very detrimental to your equipment’s rubber o-rings.