Balance

Pool Water Chemistry

The key chemical parameters and how to keep water balanced.

~8 min read·3 sections·4 key terms

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pH

pH measures how acidic or basic the water is (scale 0-14; 7 is neutral). Ideal pool pH is 7.2-7.8 (often targeted at 7.4-7.6).

pH affects swimmer comfort, disinfection efficiency, and equipment. Low pH (acidic) corrodes equipment and irritates eyes; high pH (basic) causes scaling and cloudy water and reduces chlorine effectiveness.

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Alkalinity & Calcium Hardness

• TOTAL ALKALINITY (TA) — the water's buffering capacity; it stabilizes pH. Ideal range about 80-120 ppm. Low TA causes pH to bounce; high TA makes pH hard to adjust. • CALCIUM HARDNESS — dissolved calcium; ideal about 200-400 ppm. Too low is corrosive (water 'hungry' for calcium); too high causes scaling.

Adjust alkalinity before fine-tuning pH.

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The Langelier Saturation Index

The LANGELIER SATURATION INDEX (LSI) predicts whether water is balanced, corrosive, or scaling. It combines pH, temperature, calcium hardness, and total alkalinity.

• LSI near 0 = balanced. • Negative LSI = corrosive (will dissolve surfaces/equipment). • Positive LSI = scaling (deposits calcium).

Balanced water protects swimmers, surfaces, and equipment.

📖 Key Terms

pH: Acid/base measure; ideal pool range 7.2-7.8.
Total alkalinity: The water's buffering capacity that stabilizes pH (ideal ~80-120 ppm).
Calcium hardness: Dissolved calcium; ideal ~200-400 ppm.
Langelier Saturation Index: An index predicting balanced, corrosive, or scaling water.

💡 Exam Tips

▸Ideal pool pH is 7.2-7.8 (target ~7.4-7.6).
▸Total alkalinity (~80-120 ppm) buffers and stabilizes pH.
▸Adjust alkalinity before fine-tuning pH.
▸Negative LSI = corrosive; positive LSI = scaling; near 0 = balanced.