CPO Pool Water Chemistry 2 — Questions and Answers
Question 1: What is the recommended pH range for swimming pool water according to CPO 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
The CPO-recommended pH range is 7.2–7.8, with 7.4–7.6 considered optimal for bather comfort and chlorine effectiveness.
Question 2: Which chemical is commonly used to LOWER pH in pool water?
- Sodium carbonate (soda ash)
- Sodium bicarbonate
- Muriatic acid (hydrochloric acid) (Correct answer)
- Calcium hypochlorite
Correct answer: Muriatic acid (hydrochloric acid)
Muriatic acid (hydrochloric acid) or sodium bisulfate are the standard chemicals used to decrease pool pH.
Question 3: Total alkalinity in pool water primarily serves as a buffer against changes in:
- Calcium hardness
- pH (Correct answer)
- Chlorine demand
- Total dissolved solids
Correct answer: pH
Total alkalinity resists rapid pH swings by neutralizing acids and bases, keeping pH stable.
Question 4: What is the ideal total alkalinity range for swimming pools?
- 40–60 ppm
- 80–120 ppm (Correct answer)
- 150–200 ppm
- 200–300 ppm
Correct answer: 80–120 ppm
The CPO-recommended total alkalinity range is 80–120 ppm to maintain adequate pH buffering.
Question 5: When pool pH rises above 7.8, what happens to free chlorine effectiveness?
- It increases significantly
- It remains unchanged
- It decreases significantly (Correct answer)
- It doubles
Correct answer: It decreases significantly
At pH above 7.8, hypochlorous acid (the active disinfectant) converts to the less effective hypochlorite ion, reducing sanitizing power.
Question 6: The Langelier Saturation Index (LSI) is used to determine:
- Required chlorine dosage
- Whether water is corrosive or scale-forming (Correct answer)
- Bather load capacity
- Bacteria count in pool water
Correct answer: Whether water is corrosive or scale-forming
The LSI calculates water balance by combining pH, temperature, alkalinity, calcium hardness, and TDS to predict corrosion or scale tendency.
Question 7: Which chemical is used to raise total alkalinity without significantly raising pH?
- Muriatic acid
- Sodium bisulfate
- Sodium bicarbonate (Correct answer)
- Calcium chloride
Correct answer: Sodium bicarbonate
Sodium bicarbonate (baking soda) effectively raises total alkalinity with a minimal effect on pH compared to soda ash.
CPO Pool Water Chemistry 2
What is the recommended pH range for swimming pool water according to CPO standards?