Understanding Pool Water Chemistry

Proper water chemistry is the foundation of safe commercial pool operation. Clear water is not the goal—safe, sanitized, and balanced water is. Operators must understand how pH, total alkalinity, calcium hardness, and sanitizer levels interact to protect bathers, equipment, and plaster surfaces.

The Core Parameters

• Free chlorine (or bromine): Primary disinfectant; commercial pools typically target 2–4 ppm free chlorine
• pH: Controls sanitizer effectiveness and bather comfort; ideal range 7.2–7.6 for most facilities
• Total alkalinity: Stabilizes pH; typically maintained at 80–120 ppm
• Calcium hardness: Protects plaster and grout; generally 200–400 ppm
• Cyanuric acid: Stabilizes outdoor chlorine; keep below health department limits (often 50–100 ppm)

The Langelier Saturation Index (LSI)

LSI predicts whether water is corrosive, balanced, or scale-forming. Commercial operators should calculate LSI regularly—especially after fill water changes or major chemical adjustments. Corrosive water damages heaters, metal fittings, and plaster. Scale-forming water clogs heat exchangers and creates rough surfaces that harbor bacteria.

Combined Chlorine and Breakpoint

When free chlorine reacts with organic contaminants, it forms combined chlorine (chloramines), which causes eye irritation and odor. Commercial pools must maintain combined chlorine below 0.2 ppm. When levels rise, operators must achieve breakpoint chlorination—a calculated superchlorination dose—to oxidize chloramines and restore effective disinfection.

Testing Frequency and Documentation

Health codes require testing at specified intervals—often every two hours while open. Use a reliable test kit, record all results in a chemical log, and take corrective action immediately when readings fall outside acceptable ranges. Digital test kits and automated controllers supplement but never replace operator verification.