Langelier Saturation Index (LSI)
A calculated water-balance score, not something you test directly, that predicts whether your pool water will lean toward scale-forming or corrosive.
The Langelier Saturation Index (LSI) combines pH, water temperature, calcium hardness, total alkalinity, and total dissolved solids into a single formula that estimates whether water is likely to deposit calcium scale, dissolve it, or sit in balance. An LSI near zero (roughly -0.3 to +0.3) means water is balanced. A positive number signals scale-forming water that can cloud plaster and clog equipment; a negative number signals corrosive water that can etch plaster and pit metal fittings. Because it's derived from five other readings rather than measured with a single test, LSI is best understood as a summary judgment, not a raw chemistry parameter.
Track this with Skimmer — log water tests and keep every reading in one place.
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