# The Langelier Saturation Index

Saturation Index = pH + TF + CF + AF – 12.1

pH: measured from test kit
TF: temperature factor; measured at pool
CF: calcium hardness factor, measured from test kit
AF: alkalinity factor, measured at pool

Formula Result:
Between –0.5 and 0.5 = water is balanced
Above 0.5 = water is over-saturated (scale-forming)
Below –0.5 = water is under-saturated (corrosive)

 Temperature F ° = TF Calcium Hardness = CF Total Alkalinity = AF 32° = 0.0 5 = 0.3 5 = 0.7 37° = 0.1 25 = 1.0 25 = 1.4 46° = 0.2 50 = 1.3 50 = 1.7 53° = 0.3 75 = 1.5 75 = 1.9 60° = 0.4 100 = 1.6 100 = 2.0 66° = 0.5 150 = 1.8 150 = 2.2 76° = 0.6 200 = 1.9 200 = 2.3 84° = 0.7 300 = 2.1 300 = 2.5 94° = 0.8 400 = 2.2 400 = 2.6 105° = 0.9 800 = 2.5 800 = 2.9 128° = 1.0 1000 = 2.6 1000 = 3.0 Saturation Index = pH + TF + CF + AF – 12.1

 Example: Test results: pH reading is 7.0 Water Temperature is 84° (TF is .7 from chart) Calcium Hardness reading is 300 ppm (CF is 2.1 from chart) Alkalinity reading is 25 ppm (AF is 1.4 from chart) Saturation Index = (pH) 7.0 + (TF) 0.7 + (CF) 2.1 + (AF) 1.4 – 12.1 = -0.9 Since the equation solution equals –0.9, this indicates a corrosive water condition.

Ideal readings for proper water balance:
- pH 7.2 to 7.6
- Total Alkalinity 80 to 125 ppm (parts per million)
- Calcium Hardness 200 to 400 ppm (parts per million)