Total alkalinity is a measure of the amount of alkaline substances in the water. These may cause the pH of the water to change in an uncontrolled manner. A low TA makes the water aggressive and causes rapid pH fluctuations. A high TA makes the pH difficult to adjust and causes cloudiness and lime precipitation. The guideline figure when using calcium hypochlorite (daily or shock chlorination) is 60-100 ppm (mg/l) and with trichlorisocyanuric acid (weekly chlorination) and Halobrom 90-125 ppm (mg/l).
Total alkalinity can be reduced with sodium bisulphate and increased with sodium bicarbonate.
Calcium hardness (CH)
The calcium hardness is a measure of the amount of lime dissolved in the water. Water with a CH of less than
100 ppm (mg/l) is described as soft water and draws lime out of, for example, the concrete of cast pools and tile
grouting, leading to disintegration. It also makes the water aggressive.
Water with a CH above 300 ppm (mg/l) is described as hard water and causes lime to be precipitated. Lime
precipitation causes limescale to form on the walls and pipes of the pool and in its mechanical equipment.
The guideline figure is 100-300 ppm (mg/l).
The calcium hardness can be reduced by dilution with fresh mains water and increased with calcium chloride.