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Episode 3: LSI Explained – The Number That Runs Every Pool | The Pools Scientific Podcast

Episode 3  ·  May 5, 2026
LSI Explained
The Number That Runs Every Pool
? Apple Podcasts ? Spotify

Most pool owners test pH and chlorine. Some test alkalinity. Almost nobody tests for the single number that ties all of those together and actually predicts whether your pool is damaging itself.

That number is the Langelier Saturation Index. This episode is the full explanation — what it is, where it came from, how to calculate it, and why it belongs at the center of every chemistry decision you make.

In This Episode
01
What the LSI Actually Is
A single number that predicts whether your water is corrosive, balanced, or scale-forming — and what each of those states means for your pool.
02
The Five Variables
pH, temperature, calcium hardness, total alkalinity, and TDS — how each one moves the index and which one carries the most weight.
03
Where It Came From
Wilfred Langelier, 1936. The history of an index that was designed for municipal water pipes — and how the pool industry adopted and adapted it.
04
The Adjustment Sequence
Alkalinity first. pH second. Calcium hardness last. Why the order matters and what happens when you get it wrong.
05
What It Looks Like on a Real Pool
A Kansas City pool, real numbers, real LSI calculation — and what the index reveals that individual parameters miss entirely.
What You’ll Take Away
  • Why testing pH and chlorine alone gives you an incomplete picture of your water
  • The target range for LSI and what corrosive vs. scale-forming water actually does to a pool over time
  • Why pH is the single most powerful lever in the entire index
  • The correct adjustment sequence and why skipping steps creates new problems
  • How to use PoolMath and the Orenda app to calculate LSI without doing the math by hand
Resources Mentioned
  • Episode 2: The 7.5% Rule — The Most Important Number You’ve Never Heard Of
  • PoolMath by Trouble Free Pool — LSI calculator
  • Orenda Technologies app — LSI calculator with CYA correction
Next Tuesday — Episode 4
Salt Chlorine Generators
The best chlorination method available. Here’s why it still fails. Everything the industry gets wrong about salt pools — and what the chemistry actually says.
New episodes every Tuesday.
Find us on Apple Podcasts and Spotify. Show notes and resources at poolsscientific.com.