LSI vs. Range Chemistry
Why You Should Use an LSI Calculator to Balance Your Pool Water (Not Just Range Chemistry)
When it comes to maintaining a healthy and long-lasting swimming pool, water chemistry is everything. For years, pool owners—and even many pool professionals—have relied on range chemistry: a checklist of target values for pH, alkalinity, calcium hardness, and other levels to keep pool water “balanced.” But as our understanding of water science improves, it's becoming clear that this method is limited and can even lead to unintended damage.
Enter the LSI Calculator.
The Langelier Saturation Index (LSI) is a smarter and more precise way to balance water. Rather than evaluating individual parameters in isolation, the LSI evaluates how those parameters interact. With an LSI calculator, pool owners and technicians can manage water chemistry in a way that’s more accurate, more protective, and more sustainable—for both the pool and the people using it.
What Is the LSI?
The Langelier Saturation Index (LSI) is a water balance equation that measures the saturation of calcium carbonate in water. In simple terms, it tells you whether your water is:
Balanced (LSI = 0): Water is in equilibrium—neither dissolving nor depositing calcium.
Aggressive (LSI < 0): Water is under-saturated and will try to gain calcium by corroding pool surfaces and equipment.
Scale-forming (LSI > 0): Water is over-saturated and will try to lose calcium by depositing scale.
The LSI formula factors in:
pH
Total Alkalinity (adjusted for cyanuric acid)
Calcium Hardness
Water Temperature
Total Dissolved Solids (TDS)
This interconnected model provides a much clearer and more reliable picture of water health than the traditional method of checking each parameter individually.
Range Chemistry vs. LSI: What’s the Difference?
Range Chemistry is a simplified checklist like this:
pH: 7.2–7.8
Total Alkalinity: 80–120 ppm
Calcium Hardness: 200–400 ppm
CYA: 30-50 ppm
While these values serve as decent guidelines, they don’t take into account how the variables influence one another. For instance, high alkalinity with low pH might still result in balanced water, but range chemistry would flag both as problematic. LSI gives a nuanced, integrated assessment.
Why LSI Is Better:
Prevents surface damage: Aggressive water etches plaster and corrodes metal components.
Prevents scale formation: Over-saturated water leaves calcium deposits on surfaces and inside equipment.
Improves water clarity and sanitizer efficiency: Balanced water helps your pool stay clean and clear.
Reduces costs: Proper balance lowers the risk of expensive repairs or premature equipment replacement.
The Dangers of Aggressive Water (LSI Too Low)
When the LSI drops below zero—especially below -0.3—water becomes aggressive. This means it will try to "pull" calcium from any available source to reach equilibrium.
What happens in aggressive water:
Etching of pool surfaces: Water extracts calcium from plaster, making it rough and worn.
Grout degradation: Tile grout deteriorates, leading to loose tiles and leaks.
Metal corrosion: Heaters, ladders, light rings, and other metal components begin to corrode.
Shortened equipment lifespan: Aggressive water wears out heaters, pumps, salt systems, and fittings.
The result? A pool that’s more expensive to maintain, with a shorter lifespan for finishes and equipment.
The Dangers of Scale-Forming Water (LSI Too High)
While aggressive water eats away at your pool, scale-forming water leaves behind unwanted deposits. If your LSI is too high—generally above +0.3—your water is trying to lose calcium to return to equilibrium. This excess calcium carbonate comes out of solution and attaches to surfaces and internal components.
What happens in scale-forming water:
Calcium scale on tile and plaster: White or grayish chalky buildup that’s tough to remove and visually unappealing.
Scaling in heaters: Heat exchangers become coated in scale, reducing efficiency and increasing energy bills.
Salt chlorine generator failure: Scale deposits coat the plates in salt cells, drastically shortening their lifespan.
Reduced circulation: Scale buildup can narrow internal plumbing and affect water flow, putting stress on the pump system.
Cloudy water: Excess calcium precipitating out of solution can cause turbidity and reduce water clarity.
In short, scale-forming water compromises both aesthetics and functionality—and leads to unnecessary repair and replacement costs.
At Sunrise Pool & Spa, we’ve seen firsthand the damage that imbalanced water can cause—etched plaster, cloudy water, scaled heaters, and corroded salt systems. That’s why we don’t rely solely on outdated range chemistry to evaluate pool water. We use the LSI method to get a full, accurate picture of your pool’s water balance.
Using an LSI calculator allows us to protect your investment by preventing costly damage before it starts.
Let us help you keep your water balanced the right way—scientifically, sustainably, and professionally.
Ready to have your pool water tested the right way?
Contact Sunrise Pool & Spa today for expert water analysis and LSI balancing services.
Because your pool deserves more than guesswork.