CPO Case Analysis & Practical Application 2 — Questions and Answers
Question 1: A pool operator notices the water is cloudy and the filter pressure gauge reads 12 psi above the clean starting pressure. What is the FIRST corrective action?
- Add clarifier to coagulate particles
- Backwash or clean the filter (Correct answer)
- Increase chlorine dosage by 50%
- Drain and refill the pool
Correct answer: Backwash or clean the filter
A filter pressure reading 8–10 psi above the clean baseline indicates the filter is dirty and should be backwashed or cleaned before other treatments.
Question 2: During a routine inspection a CPO finds the pool pH is 8.4 and chlorine residual is 1.5 ppm. Swimmers report eye irritation. What is the most likely cause?
- Chlorine level is too high for safe swimming
- High pH is reducing the effectiveness of the available chlorine (Correct answer)
- Cyanuric acid is absent from the water
- The pool needs superchlorination immediately
Correct answer: High pH is reducing the effectiveness of the available chlorine
At pH 8.4 only about 3% of chlorine exists as hypochlorous acid (the active sanitizer), making it far less effective and potentially causing irritation due to inadequate disinfection.
Question 3: A hotel spa pool holds 2,000 gallons and the bather load is 10 people at a time. The required turnover rate is 30 minutes. What minimum flow rate must the circulation pump deliver?
- 33 GPM
- 50 GPM
- 67 GPM (Correct answer)
- 100 GPM
Correct answer: 67 GPM
Flow rate = volume ÷ turnover time = 2,000 gal ÷ 30 min ≈ 67 GPM.
Question 4: A CPO measures total alkalinity at 40 ppm. Which condition is MOST likely to result from this reading?
- Scaling on pool surfaces and equipment
- pH drift and difficulty maintaining stable pH (Correct answer)
- Rapid chlorine consumption
- Algae bloom within 24 hours
Correct answer: pH drift and difficulty maintaining stable pH
Low total alkalinity (below 80 ppm) acts as a poor buffer, causing rapid and unpredictable pH fluctuations that are hard to control.
Question 5: After a fecal incident involving formed stool in a public pool, what is the recommended free chlorine level and contact time for remediation according to CDC guidelines?
- 1 ppm for 30 minutes at pH 7.5
- 2 ppm for 25 minutes at pH 7.5 (Correct answer)
- 10 ppm for 30 minutes at pH 7.5
- 20 ppm for 8 hours at pH 7.5
Correct answer: 2 ppm for 25 minutes at pH 7.5
CDC recommends raising free chlorine to 2 ppm and maintaining it for 25 minutes at pH 7.5 or below to inactivate pathogens from a formed-stool fecal incident.
Question 6: A pool's Langelier Saturation Index (LSI) is calculated at +0.8. What problem is MOST likely to develop?
- Corrosion of metal fittings and etching of plaster
- Scale deposits on pool surfaces and equipment (Correct answer)
- Algae growth due to low sanitizer demand
- Rapid loss of total alkalinity
Correct answer: Scale deposits on pool surfaces and equipment
An LSI above +0.3 indicates oversaturated water that is prone to forming calcium carbonate scale on surfaces and heat exchangers.
Question 7: An outdoor pool has cyanuric acid (CYA) at 120 ppm. What action should the operator take?
- Add more CYA to protect chlorine from UV degradation
- No action needed — CYA above 100 ppm is ideal
- Partially drain and refill the pool to dilute CYA (Correct answer)
- Superchlorinate to overcome CYA interference
Correct answer: Partially drain and refill the pool to dilute CYA
CYA above 100 ppm over-stabilizes chlorine, dramatically reducing its sanitizing ability; the only practical correction is dilution by partial drain and refill.
CPO Case Analysis & Practical Application 2
A pool operator notices the water is cloudy and the filter pressure gauge reads 12 psi above the clean starting pressure.
What is the FIRST corrective action?