Which formula represents the Langelier saturation index?

The Langelier Saturation Index (LSI) is a calculation that helps determine whether water is corrosive or scaling. It provides insight into the equilibrium of calcium carbonate in water, which is crucial for maintaining the health of pool systems.

The correct formula expresses the relationship between the pH, total alkalinity (TA), calcium hardness (CH), temperature (T), and a constant value to achieve the saturation index. In this case, the formula incorporates factors that represent the chemical properties of water that influence its corrosive or scaling potential.

The components of the formula work together to provide a numerical value: pH is a measure of the acidity or alkalinity of the water; TA helps buffer the pH and maintain stability; CH is the concentration of calcium, which impacts scaling potential; T accounts for the effect of temperature on solubility; and the constant, in this case, adjusts the overall value to reflect standard conditions.

Using the factors correctly ensures that the LSI is reflective of the water's overall tendency toward stability, corrosion, or scaling. The goal in pool management is to have the water balance at a saturation index around zero, indicating that it is neither scaling nor corrosive. Thus, the formula presented effectively captures the necessary interactions