When pH and total alkalinity, two very important measurements of swimming pool water chemistry, are too low in your pool, adding a very common household chemical to the water can solve the problem.
The pH of water is a measurement that describes whether the water is acidic or basic, stated as a number between 0 and 14. Water with a pH of 7 is neutral, neither basic nor acidic. A pH of less than 7 denotes acidity, and a pH greater than 7 indicates basicity.
The pH level of swimming pool water is important because chlorine, the most commonly used pool disinfectant, becomes less effective as pH rises. In general, the ideal pH level of swimming pool water is between 7.2 and 7.8, and when the level is above that range, the disinfecting power of chlorine is reduced significantly. Low pH can have detrimental effects, as well; acidic water can cause swimmer discomfort and damage to pool equipment and surfaces.
The total alkalinity of pool water is a measure of the concentration of alkaline substances in the water. These substances act as a buffer against changes in water pH, and when the pool's total alkalinity is in the ideal range, generally between 80 and 120 parts per million, the pH of the water tends to remain stable in its ideal range. When total alkalinity is too low, pH may fluctuate and be difficult to maintain at the correct level.
Effect of Baking Soda
Baking soda, which is a common name for the chemical compound sodium bicarbonate, is an alkaline substance that, when added to pool water, will raise the water's total alkalinity. Using baking soda to raise the water's alkalinity to the desired level will usually also cause the water's pH level to stabilize in the optimal range.
When a pool test kit indicates that the water's pH is below the desired level and the total alkalinity level is also too low, adding baking soda to the pool can help bring both measurements back in line.
If pH is low but total alkalinity is in the correct range or too high, adding baking soda will likely push total alkalinity above the desired range; instead, add sodium carbonate, also called soda ash, which will raise pH without significantly affecting total alkalinity.
If pH is too high, use an acidic pH reducer, often muriatic or hydrochloric acid, rather than either baking soda or soda ash. After lowering the pH to the correct level, check the pool's total alkalinity and if it is too low, use baking soda to bring the measurement back up.
Using Baking Soda
To use baking soda to raise total alkalinity and pH, add 1 1/2 pounds of baking soda per 10,000 gallons of water to raise total alkalinity by 10 parts per million. Adding too much baking soda at one time can raise alkalinity and pH too quickly, so add only this much at one time.
Retest pH and total alkalinity within six to 24 hours and add more baking soda if necessary to raise alkalinity further. Once total alkalinity is in the correct range, the pool's pH should also stabilize in the correct range within a few days.