NASCO Water Chemistry & Quality Control 3 — Questions and Answers
Question 1: Which condition is MOST likely to cause a rapid drop in pool water pH?
- High bather load producing sweat and urine
- Heavy rain diluting pool water (Correct answer)
- Adding sodium bicarbonate
- Low turnover rate
Correct answer: Heavy rain diluting pool water
Heavy rainfall, which is slightly acidic, dilutes the pool and introduces acid that lowers pH rapidly.
Question 2: Breakpoint chlorination requires adding chlorine to reach how many times the combined chlorine level?
- 3 times
- 7.6 times (Correct answer)
- 10 times
- 2 times
Correct answer: 7.6 times
Breakpoint chlorination requires adding enough chlorine so that free chlorine reaches approximately 7.6 times the combined chlorine level to destroy chloramines.
Question 3: What is the primary purpose of maintaining proper calcium hardness in pool water?
- To increase chlorine effectiveness
- To prevent corrosion of surfaces and equipment (Correct answer)
- To lower pH naturally
- To reduce algae growth
Correct answer: To prevent corrosion of surfaces and equipment
Proper calcium hardness (200–400 ppm) prevents corrosive water from dissolving calcium from plaster, grout, and metal fittings.
Question 4: What health hazard is most directly associated with elevated combined chlorine (chloramine) levels?
- Cryptosporidium infection
- Eye and respiratory irritation (Correct answer)
- Legionella growth
- E. coli contamination
Correct answer: Eye and respiratory irritation
Chloramines, especially nitrogen trichloride, are responsible for the characteristic 'pool smell' and cause eye, skin, and respiratory irritation.
Question 5: Which factor does NOT directly affect the chlorine demand of a pool?
- Bather load
- Sunlight exposure
- Pool depth (Correct answer)
- Presence of algae
Correct answer: Pool depth
Pool depth does not directly affect chlorine demand; bather load, sunlight (UV), algae, and organic contaminants all consume chlorine.
Question 6: For an indoor aquatic facility, what is the recommended maximum level for combined chlorine to ensure air quality?
- 1.0 ppm
- 0.4 ppm (Correct answer)
- 0.2 ppm
- 2.0 ppm
Correct answer: 0.4 ppm
Many health codes and NASCO guidelines recommend keeping combined chlorine below 0.4 ppm at indoor pools to protect air quality.
Question 7: An OTO (orthotolidine) test kit measures which water parameter?
- Total alkalinity
- Total chlorine only (Correct answer)
- pH and alkalinity
- Calcium hardness
Correct answer: Total chlorine only
OTO reagent reacts with all forms of chlorine (free and combined) to measure total chlorine; it cannot distinguish free from combined chlorine.
NASCO Water Chemistry & Quality Control 3
Which condition is MOST likely to cause a rapid drop in pool water pH?