CPI Water Balance & Chemical Testing 2 — Questions and Answers
Question 1: What is the recommended pH range for pool water according to most health codes and APSP standards?
- 6.8–7.2
- 7.2–7.8 (Correct answer)
- 7.8–8.2
- 6.5–7.0
Correct answer: 7.2–7.8
A pH of 7.2–7.8 is the standard recommended range, balancing sanitizer effectiveness and bather comfort.
Question 2: When testing total alkalinity, a result of 40 ppm would most likely cause which problem?
- Scale formation on pool surfaces
- Rapid, uncontrolled pH fluctuations (Correct answer)
- Excessive chlorine demand
- Green water discoloration
Correct answer: Rapid, uncontrolled pH fluctuations
Low alkalinity (below 80 ppm) removes pH buffering capacity, causing pH to swing dramatically with minor chemical additions.
Question 3: A DPD test kit measures which pool chemical parameter?
- Calcium hardness
- Cyanuric acid
- Free available chlorine (Correct answer)
- Total dissolved solids
Correct answer: Free available chlorine
DPD (N,N-diethyl-p-phenylenediamine) reagent reacts with free available chlorine to produce a pink color for colorimetric testing.
Question 4: Which reagent is used in the FAS-DPD test method to determine the exact chlorine concentration by titration?
- Sodium thiosulfate
- Ferrous ammonium sulfate (Correct answer)
- Sodium carbonate
- Orthotolidine
Correct answer: Ferrous ammonium sulfate
FAS (ferrous ammonium sulfate) is the titrant that decolorizes the DPD-chlorine complex, allowing precise chlorine measurement.
Question 5: A pool inspector observes milky white water in a freshly filled pool with a calcium hardness reading of 650 ppm. The MOST likely cause is:
- Algae bloom beginning
- Calcium carbonate precipitation (Correct answer)
- High cyanuric acid concentration
- Insufficient sanitizer
Correct answer: Calcium carbonate precipitation
Extremely high calcium hardness combined with adequate alkalinity and pH can cause calcium carbonate to precipitate out of solution, creating cloudy water.
Question 6: What effect does high cyanuric acid (stabilizer) have on chlorine's ability to kill pathogens?
- It has no effect on chlorine efficacy
- It increases chlorine's killing speed
- It reduces the concentration of active hypochlorous acid (Correct answer)
- It converts chlorine to a safer form
Correct answer: It reduces the concentration of active hypochlorous acid
Cyanuric acid binds free chlorine, reducing the proportion of active hypochlorous acid (HOCl) and slowing disinfection rates.
Question 7: When using test strips to check pool chemistry, the inspector should dip the strip and read results after how long?
- Immediately upon removing from water
- After 15–30 seconds as directed by manufacturer (Correct answer)
- After 5 minutes
- After the strip completely dries
Correct answer: After 15–30 seconds as directed by manufacturer
Test strip manufacturers typically specify a 15–30 second reaction time before comparing the color pads to the reference chart.
CPI Water Balance & Chemical Testing 2
What is the recommended pH range for pool water according to most health codes and APSP standards?