New York Codes, Rules and Regulations
Title 10 - DEPARTMENT OF HEALTH
Chapter I - State Sanitary Code
Part 6 - Swimming Pools, Bathing Beaches And Recreational Aquatic Spray Grounds
Subpart 6-1 - Swimming Pools
Operation, Supervision and Maintenance
Section 6-1.30 - Saturation index for swimming pools
Saturation index is equal to the pH plus a temperature factor, plus a calcium hardness factor, plus an alkalinity factor, minus the constant 12.1.
S.I. = pH + TF + CF + AF - 12.1
The optimum saturation index is zero.
Tolerance limits are plus or minus 0.5.
If the index is positive (+), the water is super-saturated with CaCO3 and may deposit a protective coating or scale in the pipeline, particularly metal filters, valves and pumps.
If the index is negative (-), water will dissolve CaCO3 and may be corrosive.
| Temp. (in °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 |
Example: Given temperature 68°, total hardness 200 mg/l, total alkalinity 20 mg/l, CaCO3 and pH = 7.8 S.I. = pH + TF + *CF + AF - 12.1 * (Calcium hardness - 0.70 × 200 = 140 mg/l.) S.I. = 7.8 + 0.52 + 1.76 + 1.22 - 12.1 = (-)0.8 Therefore, the water is corrosive................
Note: Saturation index must be maintained slightly on the positive side within the tolerance limits.
| Normal Control Levels: | |
| pH: 7.4 - 7.8 | free chlorine: 0.6 (minimum) |
| temperature: 78° - 80° (indoor) | saturation index: (-)0.5 - (+)0.5 |
| total alkalinity: 80 - 120 mg/l | calcium hardness: 180 - 250 mg/l |
Alkalinity control:
to increase - 1 1/2 lb of sodium bicarbonate NaHCO 3 baking soda will raise the alkalinity of 10,000 gallons of water by 10 mg/l.
to lower - add muriatic acid no more than one pint ( 1/8 gallon) per 5,000 gallons of pool water will lower alkalinity by 12 mg/l (or, add 1.25 lb of sodium bisulfate).
pH:
to increase - use soda ash.
to decrease - muriatic acid or sodium bisulfate.
Hardness Control: Calcium hardness is assumed to be 70% of total hardness.
to increase - 1 lb of calcium chloride will raise the calcium hardness of 10,000 gallons of water by 11 mg/l. It should be added in small amounts. To lower, dilute with soft water.
