Why Water Chemistry Is the Foundation of Pool Safety
In over three decades of aquatic safety training — from Florida municipal pools to Olympic facilities — I've seen one pattern repeat itself constantly: operators who eyeball the water, guess at chemicals, and react to problems rather than prevent them.
The good news? Proper water chemistry testing takes about 5 minutes. The bad news? Most people are doing it wrong.
What Are You Actually Testing For?
Commercial pool operators need to monitor these parameters at minimum:
- Free Chlorine (FC): 1–3 ppm for most facilities. This is your primary sanitizer.
- pH: 7.4–7.6. Too low = irritating. Too high = chlorine becomes ineffective.
- Total Alkalinity (TA): 80–120 ppm. Acts as a pH buffer.
- Cyanuric Acid (CYA): 30–50 ppm for outdoor pools. Protects chlorine from UV degradation.
- Combined Chlorine (CC): Should be below 0.2 ppm. High CC means chloramines — that "pool smell" is actually a chemistry problem, not clean water.
The Right Testing Sequence
Order matters. Always test in this sequence:
- Free and Combined Chlorine first (before pH — chlorine affects DPD test accuracy)
- pH second
- Total Alkalinity third
- Cyanuric Acid (weekly is fine, not daily)
- Calcium Hardness (monthly for most facilities)
The Most Common Mistakes I See
Mistake #1: Testing from the skimmer
Water near the skimmer is freshly returned and doesn't represent the pool's average chemistry. Take samples from elbow-depth at the midpoint of the pool, away from returns.
Mistake #2: Testing at the wrong time
Test before adding chemicals, not after. And test at the same time each day — chemistry shifts throughout the day as bathers load increases and sunlight burns off chlorine.
Mistake #3: Ignoring combined chlorine
If your free chlorine is fine but combined chlorine creeps above 0.2 ppm, you have a chloramine problem. The solution isn't more chlorine — it's superchlorination (breakpoint chlorination) to destroy the chloramines entirely.
Test Kit vs. Test Strips: What Should You Use?
For commercial facilities, a DPD reagent test kit (like the Taylor K-2006) is the professional standard. Test strips are fine for homeowners but lack the precision required for commercial compliance.
Why? State health departments require accurate readings to ±0.2 ppm. Most test strips can't consistently deliver that.
How Often Should You Test?
Minimum commercial requirements by most state health codes:
- Before opening: Full chemistry check
- Every 2 hours during operation: Chlorine and pH
- After heavy bather load or weather events: Full check
- Weekly: Cyanuric acid, calcium hardness
I recommend testing more frequently than required — especially in Florida's heat, where chlorine burns off fast and pH can swing quickly.
What to Do When Numbers Are Off
Make adjustments incrementally. Adding large doses of chemicals to "catch up" creates wild swings that are harder to manage than gradual drift. The rule I teach in every CPO class: treat pools like patients, not like emergencies.
When in doubt, close the facility. A closed pool is an inconvenience. A poorly sanitized pool is a liability — and potentially a tragedy.