Saturation Index
In order to balance the water in your pool, you will need the following readings and then use the formula & chart to get your answer. Notice that Chlorine & stabilizer in nowhere to be found in the formula.
Total Dissolved Solids, Alkalinity, Ph, Calcium, Water Temperature
The ranges that most pool stores give for their interpretation of water balance is not even close to the truth. Remember they are in business to sell pool chemicals, not making your pool experience easy or inexpensive.
| Saturation Index factors | |||||
| Water | Temperature | Calcium | Calcium | Total | Alkalinity |
| Temperature (F) | Factor | Hardness (ppm) | Factor | Alkalinity (ppm) | Factor |
| 32 | 0.0 | 25 | 1.0 | 25 | 1.4 |
| 37 | 0.1 | 50 | 1.3 | 50 | 1.7 |
| 46 | 0.2 | 75 | 1.5 | 75 | 1.9 |
| 53 | 0.3 | 100 | 1.6 | 100 | 2.0 |
| 60 | 0.4 | 125 | 1.7 | 125 | 2.1 |
| 66 | 0.5 | 150 | 1.8 | 150 | 2.2 |
| 76 | 0.6 | 200 | 1.9 | 200 | 2.3 |
| 84 | 0.7 | 250 | 2.0 | 250 | 2.4 |
| 94 | 0.8 | 300 | 2.1 | 300 | 2.5 |
| 105 | 0.9 | 400 | 2.2 | 400 | 2.6 |
| 800 | 2.5 | 800 | 2.9 | ||
TDS factor
1,000 PPM or less = 12.1
1,000 ppm - 2,000 ppm = 12.2
Over 2,000 ppm = 12.3
Formula
.[ Temp Factor (TF) + Calcium Factor (CF) + Alkalinity Factor (AF) + Ph ] - TDS factor
TF + CF + AF + PH - TDS factor
Extreme corrosive = - 0.3 or greater (will cause damage to pool surface)
Slightly Corrosive = - 0.1 (good)
Balanced = 0.0 (excellent)
Slightly Scale forming = +0.1 (good)
Example
Ph = 7.5
Calcium = 125
Alkalinity = 150
Temp = 84
TDS 900 ppm
7.5 (PH)+ 1.7 (CF) + 2.2 (AF) + 0.7 (TF) = 12.1
12.1 (total) -12.2 (tds factor) = 0 therefor the pool water is in a balanced state