12
Calculating the Saturation Index
The saturation index is a formula that relates pH, calcium and alkalinity in the pool water. A well balanced
pool water will have a formula result range between -0.3 and 0.3 Outside this range, the pool water is out of
balance, potentially damaging pool equipment or scaling the SCG.
The equation to calculate Si is:
SI = pH + CHF + AF + TF + TDSF
Saturation
Index
pH as
tested
Calcium
Hardness
Factor
Alkalinity
Factor
Tempera-
ture
Factor
TDS
Factor
Cyanuric acid in the form of cyanurate ions contribute to alkalinity. Thus, a correction must be made to total
alkalinity. We subtract 1/3 of the cyanuric acid level from the reading obtained in the total alkalinity test.
Total Alkalinity - 1/3 Cyanuric Acid = Corrected Alkalinity
This correction can be considerable in established pools with high cyanuric acid levels; for example, at 240
ppm cyanuric acid, the correction amounts to 80 ppm (240 ÷ 3 = 80).
TDS Factor
(Factors shown below are based on the actual measured value for the particular parameter)
TDS Factor
<1000 12.10
1000 12.19
2000 12.29
3000 12.35
4000 12.41
5000 12.44
Langelier Saturation Index Factors
Note: Use the reading closest to your actual reading in choosing the factor.
Total alkalinity in this context refer to the total of carbonate and bicarbonate alkalinity. If cyanuric
acid is used, a correction factor must be used (see cyanuric acid Table 2 on page 14).
IntelliChlor Salt Chlorine Generator Installation and User’s Guide
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