The Saturation Index is the key to understanding pool water chemistry under a wide variety of conditions.
The Saturation
Index sometimes called the Langlier Index or Water Balance Index,
is the driving force for determining if a pool is balanced. An unbalanced
pool is either acidic(corrosive) or basic(scaling) . The index determines
whether the water is balance or not. Water can be balanced, even though
it may not meet "traditional" values for being balance. Local
water supplies have an influence on the water chemistry.
Saturation Index Equation: SI = pH + TF + CF + AF -TDS
TF
CF
AF
TDS |
=
Temperature Factor in degrees Fahrenheit
= Calcium Hardness Factor in ppm Calcium Carbonate
= Alkalinity Factor
= 12.07 for Total Dissolved Solids(TDS) factor for TDS 500ppm
= 12.10 for Total Dissolved Solids(TDS) factor for TDS 1000 ppm
= 12.2 for Total Dissolved Solids(TDS) factor for TDS 1000-2000ppm
= 12.2 for Total Dissolved Solids(TDS) factor for TDS >2000
ppm |
To
Calculate the Saturation Index, test for pH, temperature, calcium
hardness and total alkalinity. Find the corresponding values in the
chart below and enter those into the equation. Acceptable values
are -0.3 to +0.3, ideally 0.0 to +0.3.
Note: Take your value from each column. Match you temperature to get TF, Your Calcium to get CF and Alkalinity to get AF |
Temperature
|
Calcium
Hardness
|
Total
Alkalinity
|
Temp |
TF |
ppm |
CF |
ppm |
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 |
1.7 |
150 |
2.2 |
76 |
0.6 |
200 |
1.9 |
200 |
2.3 |
80 |
0.7 |
300 |
2.1 |
250 |
2.4 |
94 |
0.8 |
400 |
2.2 |
300 |
2.5 |
105 |
0.9 |
800 |
2.5 |
600 |
2.8 |
Sample Results:
pH 7.4
Temperature= 83'F
Calcium Hardness = 300ppm
Alkalinity = 100 ppm
TDS = 800 ppm
The Calculation:
SI = 7.4 + 0.7 + 2.1 + 2.0 - 12.1 = 0.1
The SI falls within an acceptable range and
the water is balanced. |
|
