Salt / TDS → CSI Impact Viewer

Understanding Salt, TDS, and CSI

Calcium Saturation Index, or CSI, estimates whether pool water is likely to form calcium scale or become aggressive toward plaster, grout, stone, and metal components. Salt and total dissolved solids are part of that calculation, but their effect is usually smaller than the effect of pH, temperature, alkalinity, and calcium hardness.

Why Salt Changes CSI

As dissolved solids increase, the water’s ionic strength changes slightly. In CSI calculations, that shift can move the final number even when pH, alkalinity, calcium hardness, and temperature remain the same. Saltwater pools therefore may show a slightly different CSI than low-salt pools with otherwise identical chemistry.

What This Viewer Shows

• The estimated CSI at your current salt level.
• How CSI changes as salt rises or falls.
• Whether the calculated water balance moves toward scaling or aggressive conditions.
• How small the salt effect is compared with the major CSI factors.

Salt Is Not the Whole TDS Number

This tool uses salt as a practical stand-in for total dissolved solids and adds a baseline amount for other dissolved material. Actual TDS also includes calcium, alkalinity, stabilizer, dissolved treatment chemicals, and minerals from source water.

Managing CSI in Salt Pools

When CSI needs adjustment, pH is usually the fastest and strongest control. Total alkalinity, calcium hardness, and water temperature also have a greater effect than modest salt changes. Do not raise or lower salt solely to control CSI unless the salt level also needs correction for the chlorine generator.