NASCO Water Chemistry & Quality Control 2 — Questions and Answers
Question 1: What is the recommended combined chlorine (chloramine) level that should trigger superchlorination or breakpoint chlorination?
- 0.1 ppm
- 0.2 ppm (Correct answer)
- 0.5 ppm
- 1.0 ppm
Correct answer: 0.2 ppm
When combined chlorine reaches 0.2 ppm or higher, breakpoint chlorination should be performed to eliminate chloramines.
Question 2: The Langelier Saturation Index (LSI) is used to determine which water condition?
- Chlorine demand
- Water balance and corrosivity/scale potential (Correct answer)
- Cyanuric acid effectiveness
- Alkalinity buffering capacity
Correct answer: Water balance and corrosivity/scale potential
The LSI measures whether pool water is balanced, corrosive, or scale-forming based on pH, alkalinity, calcium hardness, and temperature.
Question 3: Which chemical is added to pool water to RAISE total alkalinity?
- Muriatic acid
- Sodium bicarbonate (Correct answer)
- Sodium carbonate (soda ash)
- Calcium chloride
Correct answer: Sodium bicarbonate
Sodium bicarbonate (baking soda) is the standard chemical used to raise total alkalinity in pool water.
Question 4: At what water temperature does chlorine lose effectiveness most rapidly?
- Below 60°F (15°C)
- Above 84°F (29°C) (Correct answer)
- At exactly 78°F (26°C)
- Below 70°F (21°C)
Correct answer: Above 84°F (29°C)
Chlorine dissipates much faster at higher temperatures (above 84°F), requiring more frequent testing and dosing.
Question 5: What does a DPD (N,N-diethyl-p-phenylenediamine) test kit measure?
- pH and alkalinity
- Free and total chlorine levels (Correct answer)
- Calcium hardness
- Cyanuric acid concentration
Correct answer: Free and total chlorine levels
DPD reagents react with chlorine to produce a color change, allowing measurement of free and total chlorine concentrations.
Question 6: Cyanuric acid (stabilizer) in outdoor pools should typically be maintained within what range?
- 0–10 ppm
- 10–30 ppm
- 30–50 ppm (Correct answer)
- 80–100 ppm
Correct answer: 30–50 ppm
Cyanuric acid is recommended at 30–50 ppm for outdoor pools to protect chlorine from UV degradation without over-stabilizing.
Question 7: When shocking a pool with calcium hypochlorite, why should it be pre-dissolved in a bucket of water before adding to the pool?
- To increase its pH
- To prevent bleaching or damage to pool surfaces (Correct answer)
- To activate cyanuric acid
- To lower chlorine demand
Correct answer: To prevent bleaching or damage to pool surfaces
Pre-dissolving calcium hypochlorite prevents concentrated product from settling on pool surfaces and causing bleaching or etching.
NASCO Water Chemistry & Quality Control 2
What is the recommended combined chlorine (chloramine) level that should trigger superchlorination or breakpoint chlorination?