Calculating The Saturation Index; How Much Salt To Use? - Pentair STA-RITE SC-75P Installation Manual

How Much Salt to Use?

FOR ALL NEWLY CONSTRUCTED OR RESURFACED PLASTER POOLS: Do not operate the SC-75 with newly poured
or resurfaced pool plaster. Salt is a corrosive element and severe salt damage can occur to your pool. Wait at
least ONE (1) MONTH after construction to allow plaster to cure before adding salt and operating SC-75. Follow the pool
surface manufacturer's guidelines for your specific pool.
FOR NEW VINYL LINER POOLS, contact the manufacturer for recommended guidelines before adding salt and operating SC-75.
Use the Table 1 chart to determine how much salt will be needed. Most pools contain some salt, depending on the water
source and chemicals used for sanitizing. Therefore, the pool owner must always test salt levels before adding salt. A hand
held meter calibrated for NaCl (salt) can be used to determine the salt levels of the pool water. After the SC-75 Salt Chlorinator
is powered on, the LED salt level lights will blink from bottom to top for two (2) minutes while it analyzes the pool water,
then the LED indicators will show one (1) of four (4) salt level ranges. This solid light indicates the salt status of the pool.
• 3000 to 3500 ppm of salt is recommended for optimum water conditions.
• Low salt concentration below 2600 ppm will cause the unit to turn off
• High salt concentration above 4500 ppm may cause excessive corrosion or deterioration to pool equipment and
surrounding surfaces in and around the pool.
Note: Salt measurements will vary between measuring devices (salt test strips, electronic testers, and titration). The salt sensor
reading is within +/- 500 ppm accuracy. For more troubleshooting information about high salt levels, see "Troubleshooting".

Calculating the Saturation Index

The saturation index is a formula that relates pH, calcium and alkalinity in the pool water. A well balanced pool water will
have a formula result range between -0.3 and 0.3 Outside this range, the pool water is out of balance, potentially damaging
pool equipment or scaling the SC-75. The equation to calculate Si is:
SI = pH +
Saturation
Index
Cyanuric acid in the form of cyanurate ions contribute to alkalinity. Thus, a correction must be made to total alkalinity. We
subtract 1/3 of the cyanuric acid level from the reading obtained in the total alkalinity test.
Total Alkalinity - 1/3 Cyanuric Acid = Corrected Alkalinity
This correction can be considerable in established pools with high cyanuric acid levels; for example, at 240 ppm cyanuric
acid, the correction amounts to 80 ppm (240 ÷ 3 = 80).
TDS Factor (Factors shown below are based on the actual measured value for the particular parameter)
TDS Factor
<1000 12.10
1000 12.19
2000 12.29
3000 12.35
4000 12.41
5000 12.44
CHF + AF + TF +
pH as Calcium
tested Hardness
Factor
11
Alkalinity Temperature
Factor Factor
TDSF
TDS
Factor