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10.2 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:
pH as tested
Plus the Temperature factor
Plus the Calcium Hardness factor
Plus the Alkalinity factor
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
CALCIUM
HARDNESS
CF
TOTAL
ALKALINITY
AF
SALT LEVEL
TDSF
60ºF
15.6ºC
0.4
150 ppm (mg/L)
1.8
075 ppm (mg/L)
1.9
0000 - 1000 ppm (mg/L)
12.1
66ºF
18.9ºC
0.5
200 ppm (mg/L)
1.9
100 ppm (mg/L)
2.0
1001 - 2000 ppm (mg/L)
12.2
76ºF
24.4ºC
0.6
250 ppm (mg/L)
2.0
125 ppm (mg/L)
2.1
2001 - 3000 ppm (mg/L)
12.3
84ºF
28.9ºC
0.7
300 ppm (mg/L)
2.1
150 ppm (mg/L)
2.2
3001 - 4000 ppm (mg/L)
12.4
94ºF
34.4ºC
0.8
400 ppm (mg/L)
2.2
200 ppm (mg/L)
2.3
4001 - 5000 ppm (mg/L)
12.5
103ºF
39.4ºC
0.9
600 ppm (mg/L)
2.4
250 ppm (mg/L)
2.4
5001 - 6000 ppm (mg/L)
12.6
Table 8
Example:
WATER TEST RESULTS
FACTORS
WATER SATURATION
pH = 7.8
pH = 7.8
SI = 0.8
Water is scale forming and needs to
be balanced
Temperature is 84°F
TF = 0.7
Calcium Hardness is 600 ppm (mg/L)
CF = 2.4
Total Alkalinity is 200 ppm (mg/L)
AF = 2.3
Salt is 3500 ppm (mg/L)
TDSF = 12.4
Corrosive to metals,
etches plaster
finishes, and irritates
skin.
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
Scaling, staining, and
cloudy water conditions.
OK
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.
