Water chemistry
Langelier Saturation Index
The Langelier Saturation Index is a number that predicts whether pool water will scale or etch surfaces.
The Langelier Saturation Index, or LSI, combines pH, alkalinity, calcium, temperature, and dissolved solids into one score. A score near zero means balanced water. A negative score means the water is hungry for minerals and can etch plaster. A positive score means it tends to drop scale.
Heat pushes the score up, so summer pools in North Texas lean toward scale. You do not need to do the math by hand. Most pool apps and service tests report it. If it is off, adjust pH, alkalinity, or calcium in that order.
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