Pool, Spa & Water Treatment Chemistry worked example

Free Chlorine Adjustment with target free chlorine of 13 ppm: a worked example

Push target free chlorine up to 13 ppm and the picture changes. This example computes every intermediate figure at that operating point. Use it to decide whether a sanitizer adjustment is still needed after accounting for a planned dose.

The inputs for this scenario

  • Target free chlorine: 13 ppm (raised for this scenario; the documented default is 5)
  • Current free chlorine reading: 2 ppm (unchanged)
  • Chlorine credit from scheduled dose: 0 ppm (unchanged)
  • Free-chlorine reserve above target: 0 ppm (unchanged)

Working through the calculation

  • Applying the documented formula (Remaining chlorine gap = target free chlorine - current free chlorine - planned credit + reserve) to the inputs above produces each figure below.
  • At this operating point the engine returns 11 ppm for remaining free-chlorine gap, the number this scenario is built around.
  • At this operating point the engine returns 2 value for current and planned chlorine.
  • At this operating point the engine returns 13 value for target free chlorine.
  • At this operating point the engine returns 84.62 % for utilization.

How this compares with the baseline

  • Against the tool's baseline example, where target free chlorine sits at 5 ppm and the headline result is 3 ppm, this scenario comes in 267% above the baseline at 11 ppm.
  • It computes the remaining free-chlorine gap in ppm as target FC minus current FC minus any scheduled chlorine credit, plus any reserve you want to hold above target. The value of this scenario is the size of the gap it exposes: that gap, priced out over a year, is the budget you can justify spending to close it.

Results at a glance

  • Remaining free-chlorine gap: 11 ppm (headline result)
  • Current and planned chlorine: 2 value
  • Target free chlorine: 13 value
  • Utilization: 84.62 %

Run it with your numbers

  • Every input above is editable in the live Free Chlorine Adjustment calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.