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Using the Saturation Index
This index is used by pool professionals to ensure that your total water chemistry does not fall
into a corrosive or scaling condition. Either condition can cause premature damage to the cell,
any of your other equipment, as well as your cementitious finish.
The Saturation Index is composed of the following factors:
l pH as tested
l Plus the Temperature factor
l Plus the Calcium Hardness factor
l Plus the Alkalinity factor
l Minus the Total Dissolved Solids factor (in this case the bulk of the dissolved solids are salt)
This is expressed in the formula SI = pH + TF + CF + AF – TDSF and uses the following charts:
TEMPERATURE
TF
60°F 15.6°C 0.4
66°F 18.9°C 0.5
76°F 24.4°C 0.6
84°F 28.9°C 0.7
94°F 34.4°C 0.8
103°F 39.4°C 0.9
CALCIUM
HARDNESS
CF
150 ppm (mg/L) 1.8
200 ppm (mg/L) 1.9
250 ppm (mg/L) 2.0
300 ppm (mg/L) 2.1
400 ppm (mg/L) 2.2
600 ppm (mg/L) 2.4
TOTAL
ALKALINITY
AF
075 ppm (mg/L) 1.9
100 ppm (mg/L) 2.0
125 ppm (mg/L) 2.1
150 ppm (mg/L) 2.2
200 ppm (mg/L) 2.3
250 ppm (mg/L) 2.4
SALT LEVEL
TDSF
0000 - 1000 ppm (mg/L) 12.1
1001 - 2000 ppm (mg/L) 12.2
2001 - 3000 ppm (mg/L) 12.3
3001 - 4000 ppm (mg/L) 12.4
4001 - 5000 ppm (mg/L) 12.5
5001 - 6000 ppm (mg/L) 12.6
Example:
7.8 = pH as measured
0.7 = Temperature is 84°F (TF)
2.4 = Calcium Hardness is 600 ppm (mg/L) (CF)
2.3 = Total Alkalinity is 200 ppm (mg/L) (AF)
12.4 = Salt is 3,500 ppm (mg/L) (TDSF)
0.8 = Saturation Index.
This water is scale forming and needs to be balanced.
Table 3
If adjustments need to be made to balance the water, the recommended sequence is as follows:
1.
Test and adjust total alkalinity. This may reduce pH so wait at least 8 hours before proceeding.
2.
Test again and adjust pH, then
3.
Adjust calcium hardness.
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