The Langelier Saturation Index
Stable water balance quality is based on the proper use of this saturation
index and formula. Various factors are used to calculate saturation
levels (pH, total alkalinity, total hardness, total dissolved solids
and temperature). When these factors are placed into the formula, the
result provides the information needed to balance the pool water and
correct its condition.
First all parameters of the formula must be tested with the appropriate
test kits, then the applicable “factors” (see Table below)
area placed into the following formula:
Saturation Index = pH + TF + CF + AF – 12.1
pH: measured from test kit
TF: temperature factor; measured at pool
CF: calcium hardness factor, measured from test kit
AF: alkalinity factor, measured at pool
Formula Result:
Between –0.5 and 0.5 = water is balanced
Above 0.5 = water is over-saturated (scale-forming)
Below –0.5 = water is under-saturated (corrosive)
Temperature F ° = TF
|
Calcium Hardness = CF
|
Total Alkalinity = 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 = 1.8 |
150 = 2.2 |
76° = 0.6 |
200 = 1.9 |
200 = 2.3 |
84° = 0.7 |
300 = 2.1 |
300 = 2.5 |
94° = 0.8 |
400 = 2.2 |
400 = 2.6 |
105° = 0.9 |
800 = 2.5 |
800 = 2.9 |
128° = 1.0 |
1000 = 2.6 |
1000 = 3.0 |
Saturation
Index = pH + TF + CF + AF – 12.1
|
Example:
Test results:
pH reading is 7.0
Water Temperature is 84° (TF is .7 from
chart)
Calcium Hardness reading is 300 ppm (CF is 2.1 from
chart)
Alkalinity reading is 25 ppm (AF is 1.4 from chart)
Saturation Index =
(pH) 7.0 + (TF) 0.7 + (CF) 2.1 + (AF) 1.4 – 12.1
= -0.9
Since the equation solution equals –0.9,
this indicates a corrosive water condition.
|
Ideal readings for proper water balance:
- pH 7.2 to 7.6
- Total Alkalinity 80 to 125 ppm (parts per million)
- Calcium Hardness 200 to 400 ppm (parts per million)
In the next sections,
we will discuss each individual components of water balance in detail.
Click here for a printable copy of the Langelier Saturation Index table shown above.
|
|
|
Water
Balance |
|
Temperature |
|
