CPO Water Testing and Analysis 3 — Questions and Answers
Question 1: How is the combined chlorine (chloramine) level calculated from pool water test results?
- Total chlorine minus free chlorine (Correct answer)
- Free chlorine plus total chlorine
- Total chlorine divided by free chlorine
- Free chlorine multiplied by a factor of 10
Correct answer: Total chlorine minus free chlorine
Combined chlorine equals total chlorine minus free chlorine; it represents chlorine that has reacted with nitrogen compounds and lost its disinfecting power.
Question 2: What is the primary function of cyanuric acid (CYA) when added to outdoor swimming pool water?
- Increases chlorine potency at high water temperatures
- Lowers pH levels without additional chemical additives
- Protects free chlorine from degradation by UV sunlight (Correct answer)
- Increases the total alkalinity of the pool water
Correct answer: Protects free chlorine from degradation by UV sunlight
Cyanuric acid bonds with hypochlorous acid and shields it from UV radiation, significantly extending the effective lifespan of chlorine in outdoor pools.
Question 3: ORP (Oxidation-Reduction Potential), used to assess pool water disinfection efficacy, is measured in which unit?
- Millivolts (mV) (Correct answer)
- Parts per million (ppm)
- Milligrams per liter (mg/L)
- Nephelometric turbidity units (NTU)
Correct answer: Millivolts (mV)
ORP is an electrochemical measurement expressed in millivolts that indicates the overall oxidizing power and disinfection capacity of the water.
Question 4: An ORP reading of 650–750 mV in a properly maintained pool typically indicates which condition?
- Dangerous over-chlorination requiring immediate shutdown
- Insufficient disinfection posing a health risk to swimmers
- Adequate disinfection with effective pathogen control (Correct answer)
- High cyanuric acid interfering with sensor accuracy
Correct answer: Adequate disinfection with effective pathogen control
Most health authorities consider an ORP of 650–750 mV the range that provides effective pathogen inactivation in pool water.
Question 5: When the combined chlorine (chloramine) level exceeds 0.2 ppm, what is the recommended corrective action?
- Increase the cyanuric acid concentration
- Raise the pH to above 8.0 immediately
- Drain and completely refill the pool
- Perform breakpoint chlorination (superchlorination) (Correct answer)
Correct answer: Perform breakpoint chlorination (superchlorination)
Breakpoint chlorination involves adding enough chlorine to oxidize and destroy chloramines, restoring effective free chlorine levels.
Question 6: A phenol red test kit is the standard colorimetric tool used to measure which water parameter?
- pH level (Correct answer)
- Free chlorine concentration
- Total alkalinity
- Calcium hardness
Correct answer: pH level
Phenol red is a pH indicator dye that produces colors ranging from yellow (pH ~6.8) to red/violet (pH ~8.4) for visual comparison against a chart.
Question 7: Which chemical form of chlorine is responsible for causing eye and skin irritation and the characteristic 'pool smell'?
- Free chlorine (hypochlorous acid)
- Calcium hypochlorite pellets
- Combined chlorine (chloramines) (Correct answer)
- Sodium hypochlorite solution
Correct answer: Combined chlorine (chloramines)
Chloramines (combined chlorine) are the irritating byproducts formed when free chlorine reacts with ammonia and nitrogen compounds introduced by bathers.
CPO Water Testing and Analysis 3
How is the combined chlorine (chloramine) level calculated from pool water test results?