LSI Outside the Bubble — What the Scientists Really Say

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Rudy does something different this week: he takes the Langelier Saturation Index (LSI) out of the pool industry echo chamber and walks it through the lens of academics, civil engineers, groundwater chemists, and industrial water experts who don’t care about plaster warranties, brand marketing, or trade show politics.

If you’ve ever argued about “which LSI is right” in a Facebook group, this one is for you.

Episode Overview

Rudy kicks off with a news analogy:
 How the same event looks completely different on U.S. news versus international coverage. Same facts, different framing.

He uses that setup to shift how we look at LSI:

• We already know the pool industry story about LSI: PHTA charts, app calculators, Orenda talks, trade folklore.
• But this episode asks:
   “What does the scientific community think about LSI when they’re not talking to pool people at all?”

Rudy dives into how universities and researchers actually use and define LSI in research on:

• Groundwater
• Drinking water stability
• Industrial cooling systems
• Desalination plants
• Boiler operations
• Cement leaching
• Environmental engineering

Key Concepts Covered

1. LSI as the Outside World Sees It

• Academics consistently define LSI = pH − pHs, where pHs is the calculated saturation pH, not something you measure with a test kit.
• pHs is derived from:
  • Calcium hardness
  • Carbonate alkalinity
  • Ionic strength (modeled via TDS / activity coefficients)
  • Temperature
• LSI is treated as a thermodynamic index:
  • It shows which direction water wants to move with respect to calcium carbonate.
  • It does not tell you how fast scale forms, how thick it gets, or how quickly surfaces dissolve.

2. What Negative, Zero, and Positive LSI Actually Mean (Academically)

• Negative LSI
  • Water is under-saturated in calcium carbonate.
  • It is capable of dissolving calcium carbonate if given the chance.
  • Researchers call it “aggressive” or “decalcifying” water—but they do not say it guarantees corrosion.
• LSI ≈ 0
  • Theoretical equilibrium with calcium carbonate.
  • In the real world, systems almost never sit at perfect equilibrium because of flow, aeration, dosing, and turbulence.
• Positive LSI
  • Water is supersaturated with calcium carbona

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