As temperatures rise and swim season approaches, pool professionals must turn their attention to spring pool opening.

A key part of this process is ensuring that the water is properly balanced — not just in terms of pH and chlorine, but also in relation to the Langelier Saturation Index (LSI). The LSI helps determine whether water is in a corrosive, balanced, or scale-forming state, making it an essential tool for preventing damage to pool surfaces and equipment.

Is the Water in Balance After Winter?

If a pool was properly winterized, does that mean the water will be balanced in the spring? Not necessarily. Several factors can cause chemical levels to shift over the winter, even if the pool was closed correctly:

Temperature Drop and LSI Shift

The LSI is temperature dependent, meaning that as water gets colder, its balance shifts. A pool that was perfectly balanced at 80°F before closing may have become corrosive as the water temperature dropped.

If the LSI became negative (below -0.3), the water may have pulled calcium from pool plaster, causing etching or surface degradation.

Dilution from Rain and Snow

Over the winter, rain, snow, and ice melt can introduce large amounts of fresh water, diluting alkalinity, calcium hardness, and stabilizer levels. This can make the water more aggressive, increasing the risk of corrosion on metal components like ladders, heaters, and light fixtures.

Alkalinity and pH Changes

Without regular adjustments, pH can drift over the winter. If pH dropped too low, it may have contributed to etching or metal corrosion.

Total alkalinity may have decreased due to acidic precipitation (rain water tends to be acidic), further reducing the water’s buffering capacity and making pH unstable.

Calcium Hardness Shifts

If calcium levels were low before winter, any loss due to dilution could push the LSI into a corrosive range.

In some cases, scale that formed before winter could dissolve back into the water, temporarily increasing calcium hardness but potentially leading to cloudy water when temperatures rise again.

Steps for a Balanced Spring Opening

To ensure a smooth pool opening, water chemistry should be carefully tested and adjusted with the LSI in mind.

Here’s how: 1. Test Water Chemistry

• Measure pH, total alkalinity, calcium hardness, cyanuric acid (CYA), and water temperature.

• Use the LSI formula or an LSI calculator to determine if the water is balanced. Spring

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2. Adjust Alkalinity and pH First

• Total alkalinity should be 80-120 ppm for most pools.

• pH should be 7.4-7.6 for optimal water balance.

3. Correct Calcium Hardness

• If the calcium is below 200 ppm, add calcium chloride to raise levels.

• If the calcium is above 1,000 ppm, consider dilution, or use soda ash to lower calcium to prevent scaling.

4. Balance LSI Before Heating the Pool

• Cold water is more prone to corrosion, so keeping the LSI near zero before heating helps prevent damage to surfaces and equipment.

By prioritizing LSI balance during spring opening, pool pros can protect pool surfaces, reduce maintenance issues, and ensure a smooth start to the swim season.

Total Alkalinity

Total alkalinity plays a crucial role in swimming pool water chemistry, particularly in relation to the Langelier Saturation Index (LSI), which helps determine whether water is balanced, corrosive, or prone to scaling.

Why Total Alkalinity Matters in Pools

pH Buffering — Total alkalinity helps stabilize pH levels, preventing rapid fluctuations that can lead to corrosive or scale-forming conditions. When alkalinity is too low, pH can swing dramatically, making it difficult to maintain proper water balance.

Impact on LSI — The LSI is a measure of water’s saturation level with calcium carbonate. Because total alkalinity is a key factor in LSI calculations, maintaining proper alkalinity ensures that water neither corrodes pool surfaces (if too low) nor forms scale (if too high).

Preventing Corrosion — If total alkalinity is too low, the water becomes aggressive, leading to corrosion of pool surfaces, metal fixtures, and even equipment like heaters. This can result in costly repairs and equipment failures.

Preventing Scale Formation — If total alkalinity is too high, it can push the LSI into a scaling condition, leading to calcium buildup on pool surfaces, pipes, and filters, reducing circulation efficiency and increasing maintenance needs.

Total alkalinity can be thought of as a measure of the anions (negatively charged ions) in the pool that contribute to its ability to resist pH changes.

Don’t Forget To Subtract Out Cyanuric Acid

If cyanuric acid is present — and it generally is — it needs to be subtracted out of the measured total alkalinity when calculating the LSI. This is because we are actually interested in the carbonate alkalinity, and the cyanuric acid is a part of the measured total alkalinity.

To calculate carbonate alkalinity at normal pH levels, subtract out one third of the cyanuric acid concentration. In other words, total