⚗️ Pool Water Balance Calculator
Enter your pH, alkalinity, calcium hardness, temperature, and TDS to get your Langelier Saturation Index and a plain-English verdict — balanced, corrosive, or scale-forming.
💧 One Number for Balanced Water
What is a Pool Water Balance Calculator?
It takes the readings from your test kit — pH, total alkalinity, calcium hardness, water temperature, and total dissolved solids — and combines them into the Langelier Saturation Index, the industry standard for judging whether water is balanced, corrosive, or scale-forming.
Balanced water protects your plaster, tile, heater, and salt cell, and keeps chlorine working efficiently. Rather than eyeballing five separate readings, this gives you one number and a clear verdict so you know which direction to adjust — always change one factor at a time, re-test, and treat the result as guidance alongside your test kit.
❓ Frequently Asked Questions
What is the Langelier Saturation Index (LSI)?
The LSI is a single number that summarises whether your pool water is balanced with respect to calcium carbonate. It combines pH, total alkalinity, calcium hardness, temperature, and total dissolved solids into one figure. An LSI near zero means the water is in equilibrium — neither dissolving nor depositing calcium.
What LSI range is considered balanced?
An LSI between −0.3 and +0.3 is considered balanced and safe for pool surfaces and equipment. Below −0.3 the water is corrosive (aggressive): it can etch plaster, dissolve grout, and pit metal. Above +0.3 it's scale-forming: calcium deposits build up on surfaces, heaters, and salt cells, and the water can turn cloudy.
Which value should I adjust first if my water is off?
pH and total alkalinity are the quickest levers and safest to change day-to-day; calcium hardness moves more slowly and can only be lowered by draining and diluting. If the LSI is low, raising pH or alkalinity usually brings it up; if it's high, lowering pH is the common first step. Change one factor, re-test, and re-check the index.
Does water temperature really affect balance?
Yes — warmer water is more prone to scaling, so a heated spa or a pool in a summer heatwave can tip scale-forming even when the chemistry hasn't changed. That's why temperature is part of the calculation. Re-check your balance when the seasons change or after you start running a heater.