Pool, Spa & Water Treatment Chemistry worked example

LSI Water Balance with measured water ph of 3.75 pH: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop measured water ph to 3.75 pH, then walk the calculation through step by step. Estimate a simplified water-balance index from pH, alkalinity factor, calcium factor, temperature factor, and TDS factor.

The inputs for this scenario

  • Measured water pH: 3.75 pH (the input this scenario stresses; the baseline uses 7.5)
  • Total alkalinity factor: 2 index (held at the documented default)
  • Calcium hardness and temperature factor: 2.6 index (held at the documented default)
  • Saturation constant: -12.1 index (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Simplified LSI = pH + alkalinity factor + calcium and temperature factor + saturation baseline (negative).
  • Simplified LSI works out to 8.35 index at these inputs, and this is the headline figure for the scenario.
  • Element 1 works out to 3.75 index at these inputs.
  • Element 2 works out to 2 index at these inputs.
  • Element 3 + 4 works out to 2.6 index at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where measured water ph sits at 7.5 pH and the headline result is 12.1 index, this scenario comes in 30.99% below the baseline at 8.35 index.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to measured water ph, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. It is a simplified index using lookup factors, so it is only as accurate as the factor values you enter and does not replace a full method-specific LSI calculation.

Results at a glance

  • Simplified LSI: 8.35 index (headline result)
  • Element 1: 3.75 index
  • Element 2: 2 index
  • Element 3 + 4: 2.6 index

Run it with your numbers

  • To rerun this with your own numbers, open the live LSI Water Balance calculator, set measured water ph to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.