pH and total alkalinity are related. It is not possible to change one without changing the other.

Total alkalinity is the buffering capacity of water. It is also its resistance to change in pH. Too high Total alkalinity and the pH is hard to change. It is also defined as water’s ability to neutralize acid. Too low Total alkalinity and the pH changes every time any chemical is added.

The proper Total alkalinity depends on the sanitizer you are going to use. Here are the proper Total alkalinity levels for some sanitizers:

Gas chlorine, trichlor, bromine tabs – 120 – 140 ppm
Dichlor, ozone, 2-part bromine or a combination of 2 type of chlorine: 100 – 120 ppm
Cal hypo, lithium hypo, liquid chlorine: 80 – 100 ppm

You use liquid or dry acid (Muriatic which is 31.45% hydrochloric – HCl or sodium bisulfate) to lower both pH and Total alkalinity. Most people use Muriatic. You can use dry acid and 2.5 pounds are equal to 1 quart of liquid.

Remember this about pH:

1. The pH scale is logarithmic meaning that 1 whole number on the scale is a factor of 10. Therefore, it will take 10 times more acid to lower the pH from 9.0 to 8.0 than it does to lower it from 8.0 to 7.0.
2. If the Total alkalinity is very high, the acid will work first on the Total alkalinity and then the pH.

You use sodium bicarbonate (baking soda) or sodium carbonate (soda ash) to raise pH and Total alkalinity. Which one you use depends on whether you want to raise both pH and Total alkalinity or just raise Total alkalinity with a small rise in pH.

If you want to raise both pH and Total alkalinity, use soda ash.

If you want to raise Total alkalinity with a small or little rise in pH, use sodium bicarb.

The reason is this: Soda ash has a pH of 13 and it contributes to Total alkalinity. Because of its high pH, it will raise pH substantially. On the other hand, bicarb only has a pH of 8.3. Therefore adding even a lot of it will raise Total alkalinity with a small effect on pH.

You can easily determine how much acid or base to add to your pool by using the Acid Demand or Base Demand test in your test kit.