INTELLICHEM
®
Controller Installation and User’s Guide
28
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 -0.5 and 0.5 Outside
this range, the pool water is out of balance, potentially damaging pool equipment or
scaling the salt chlorine generator. The equation to calculate Si is:
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).
Sat Index Overview
(Continued)
SI = pH + CHF + AF + TF - TDSF
Saturation
Index
pH as
tested
Calcium
Hardness Factor
Alkalinity
Factor
Temperature
Factor
TDS Factor
(12.1 non-salt,
12.2 salt pools)
Saturation Index Tables (as recommended by NSPF)