Adding a base, like sodium carbonate or soda ash, raises the pH of the water and reduces the base demand. Base demand is the opposite of acid demand, which is the amount of acid required to decrease pH. In general, the total alkalinity level should be between 80 and 120 parts per million (ppm).
Bathers are most comfortable in water with a balanced pH. This is the measure of the waters acid-alkalinity balance. Water that is too acidic or alkaline causes skin irritation and damage to equipment, as well as reducing chlorines effectiveness. Low pH indicates too little alkaline in the water. Its important to know what a pools base demand is, especially if the water typically has a low pH. A base demand test can help determine this value. In this test, a standard base is added to the pH test solution drop by drop until the optimal pH level is reached. The number of drops needed in this test correspond to pounds of soda ash needed to decrease the pH. The pools water must be tested regularly to ensure that the base demand is being met.