PREPARING THE POOL WATER

Saturation Index (SI)

The Saturation Index is a formula used to predict the calcium carbonate saturation of water, that is, whether your water will precipitate, dissolve, or be in equilibrium with calcium carbonate. Your water is properly balanced if the SI is 0 ± 0.3. If your SI is greater than 0.3, scaling and staining will occur. If your SI is less than -0.3, then the water is corrosive to metallic fixtures and aggressive to plaster surfaces and vinyl liners. A high or low SI can cause premature damage to the cell, equipment or pool finish. As a general rule, higher concentrations of calcium, total dissolved solids, pH, and alkalinity all promote a greater tendency for scale. Scaling potential also increases with increasing temperature.

Use the chart below to determine your overall water balance. Test your water for pH, water temperature, Calcium Hardness, Total Alkalinity and Salt Level and use the equivalent Factors (TF, CF, AF, Constant) from the chart below to determine your Saturation Index. Adjust your chemicals to maintain balanced water.

pH + TF + CF + AF – SC = SI

Temperature

 

TF

 

 

Calcium

 

CF

 

 

Total

 

AF

 

 

Salt Level

 

SC

 

 

 

 

Hardness

 

 

 

Alkalinity

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

60oF

15.6oC

0.4

 

 

150 ppm

1.8

 

 

75 ppm

1.9

 

 

0 – 1000 ppm

12.1

 

66oF

18.9oC

0.5

 

 

200 ppm

1.9

 

 

100 ppm

2.0

 

 

1001 - 2000 ppm

12.2

 

76oF

24.4oC

0.6

 

 

250 ppm

2.0

 

 

125 ppm

2.1

 

 

2001 - 3000 ppm

12.3

 

84oF

28.9oC

0.7

 

 

300 ppm

2.1

 

 

150 ppm

2.2

 

 

3001 - 4000 ppm

12.4

 

94oF

34.4oC

0.8

 

 

400 ppm

2.2

 

 

200 ppm

2.3

 

 

4001 - 5000 ppm

12.5

 

103oF

39.4oC

0.9

 

 

600 ppm

2.4

 

 

250 ppm

2.4

 

 

5001 - 6000 ppm

12.6

 

 

 

-.3

-.2

-.1

0

.1

.2

.3

 

 

Corrosive to

 

 

 

 

 

 

 

 

 

Scaling,

metals, etches

 

 

 

 

 

 

 

 

 

staining, and

plaster

 

 

 

 

 

 

 

 

 

cloudy water

finishes, and

 

 

 

 

 

 

 

 

 

conditions

irritates skin

 

 

 

 

OK

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Examples

Water test results #1: Total Alkalinity = 125 ppm Calcium Hardness = 400 ppm pH = 7.4

Water Temperature = 84 F Salt Level = 3000 ppm

=> AF = 2.1 => CF = 2.2 => pH = 7.4 => TF = 0.7 => SC = 12.4

7.4 + 0.7 + 2.2 + 2.1 – 12.4 = 0 (Water is perfectly balanced)

Water test results #2: Total Alkalinity = 200 ppm Calcium Hardness = 600 ppm pH = 7.8

Water Temperature = 84 F Salt Level = 3000 ppm

=> AF = 2.3 => CF = 2.4 => pH = 7.8 => TF = 0.7 => SC = 12.4

7.8 + 0.7 + 2.4 + 2.3 – 12.4 = 0.8 (Water is scale forming)

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