The pH of water indicates whether it is basic (pH above 7), acidic (pH below 7) or neutral (pH equal to 7). The Centers for Disease Control and Prevention recommends a pH range of 7.2 to 7.8 for swimming pools, with 7.6 being ideal (see References 2). If the pH is below 7.2, then a basic compound such as sodium carbonate (also known as soda ash or washing soda) must be added until the pH is brought to an acceptable level.
Check the pool’s pH with the pH test kit following the kit manufacturer’s instructions. If the pH is 7.2 or higher, no further action is recommended.
Calculate the volume of the pool if it is not already known. The Health Department of Northwest Michigan offers guidance on performing this calculation (see Reference 3).
Measure the required amount of sodium carbonate. The sodium carbonate manufacturer may have supplied a scoop marked with graduations indicating ounces. If not, then the sodium carbonate must be weighed on a scale or balance. The North Carolina Department of Environmental Health recommends a dosage of 1.25 oz. (35.4 grams) for every 1,000 gallons of pool capacity to raise the pH 0.5 units (see References 4).
Add the measured amount of sodium carbonate to a bucket and fill about two-thirds full with water. Stir the mixture with a paint stirrer or other disposable stirrer until most of the sodium carbonate has dissolved, then pour the sodium carbonate solution into the deep end of the pool, as far away from the side as possible.
Wait at least 3 hours, then re-test the pool’s pH. Repeat the treatment as necessary.