Chemists know soda ash as sodium carbonate (Na2CO3), and it's such an important commodity that the Federal Reserve Board includes monthly data about its production numbers in the board's economic review. Glass, soap, and pulp and paper manufacturers are the main consumers of soda ash, but pool owners also use it to raise the pH ofpool water. It isn't as popular as baking soda (sodium bicarbonate -- NaHCO3) for this purpose, but because it has a smaller effect on total alkalinity, soda ash is the better chemical to use when the alkalinity is already high.

Pool water should be slightly alkaline.
credit: Valentina Powers on Flickr
Soda ash helps keep pool water safe for delicate skin.

The Importance of Maintaining Pool Acidity

The acidity of pool water is measured by its pH, which is a number between 1 and 14. A value below 7 indicates acidic water, while a value above 7 indicates alkaline water. Pool pros recommend keeping the water slightly alkaline, with a pH between 7.2 and 7.6. The main reason for this is that acidic water is corrosive. It etches the sides and bottom of the pool, as well as deteriorating the metal fixtures and the pool circulation equipment. Acidic water is bad for swimmers as well. It causes redness, itching and rashes, and it stings the eyes.

When Water Is Acidic, Add a Base

Pool water can become acidic after heavy use, and because chlorine evaporates more quickly in acidic water, the water may become unsanitary. Adding cyanuric acid to stabilize the chlorine lowers the pH even more, and at some point, you might have to take steps to regulate it.

Both soda ash and baking soda are strongly alkaline (basic), and as every chemist knows, adding a base to water neutralizes the acids in it. Pool maintenance pros use both chemicals to raise the pH of acidic water, and both are available from pool supply outlets, so homeowners who maintain their own pools can do the same.

Soda Ash Vs. Baking Soda: Although they both raise pH, baking soda has a stronger effect on total alkalinity than soda ash. Total alkalinity is a measure of the ability of the water to maintain a stable pH, and it should be between 80 and 120 parts per million. A TA concentration that is too high impairs the ability of chlorine to sanitize, and the water may turn cloudy. Consequently, when you want to raise the pH in a pool in which the TA concentration is already in an acceptable range, you should use soda ash. If both pH and TA are low, use baking soda.

How to Add Soda Ash

Soda ash comes in powder form in bags that can weigh up to 50 pounds. It dissolves quickly in water, so you don't need to stir the water after pouring it into the pool. Check the instructions on the bag before introducing soda ash into the pool. Some manufacturers recommend dissolving the powder in a bucket of water first. Whether you dissolve the soda ash in water or pour the powder right into the pool, avoid introducing soda ash near the skimmers. You don't want it to be sucked through the circulation system.

To calculate the proper amount of soda ash to add, determine how much you need to raise the pH, and then calculate the volume of water in your pool and consult the instructions on the container. To avoid raising the pH too much, it's a good idea to add 3/4 of the recommended amount, wait for 6 hours, test the pH and alkalinity, and add the rest if necessary.