What is Alkalinity?
Total Alkalinity is a measure of the amount of buffering capacity in the water. It acts as a shock absorber for the pH. If Total Alkalinity is too low, the water is acidic and can corrode equipment and hot tub surfaces. It also causes pH bounce. The pH will drift down and any adjustments made to it will bounce and be difficult to control. If Total Alkalinity is too high, the water is alkaline and scale buildup and cloudy water can result. The pH will tend to drift up and will be very difficult to adjust.
Total Alkalinity, like pH, is affected by environmental factors. Rain, acidic sanitizers, addition of fill water and other product applications can all change the alkalinity over time. Total Alkalinity should be tested once every three to four weeks.
Proper Total Alkalinity levels vary with the water temperature and the sanitizer used. Ideal range for Total Alkalinity is from 125 – 150 ppm. For chlorine or bromine spas, levels of Total Alkalinity up to 200 ppm are acceptable, and the high cutoff is 170 for Biguanide spas. The cutoff is slightly lower for Biguanide spas due to the foaming tendency of the product and the tendency for pH to drift upward.
High Total Alkalinity
Add PH Down over a period of several days to lower the total alkalinity to the proper level. Discontinue PH Down additions if the pH drops below 7.2. Resume the applications where you left off when pH returns to 7.4 – 7.6. pH adjustment should not be necessary, as the alkalinity will tend to pull the pH up.
If the total alkalinity is high and continues to increase, and the pH is low and does not respond to additions of Balance pH Increaser, the problem could be bicarbonate scale. This occurs when spas are not allowed to gas off properly. Trapped gases or poor ventilation in indoor spas are reabsorbed into the water and drive the pH down and the Total Alkalinity up. It can also cause the water to cloud. To balance successfully, remove any covers and/or ventilate as well as possible and begin making adjustments again. Keep the area well ventilated or the cover removed until the hot tub water balance is returned to normal. To prevent this problem, remove covers or ventilate indoor spas for several hours a day to allow gasses to escape.