CPO Disinfection and Sanitizers 2 — Questions and Answers
Question 1: Which chlorine product has the highest available chlorine content by percentage?
- Sodium hypochlorite (liquid bleach)
- Calcium hypochlorite (cal hypo)
- Trichlor (trichloroisocyanuric acid) (Correct answer)
- Sodium dichlor
Correct answer: Trichlor (trichloroisocyanuric acid)
Trichlor tablets contain approximately 90% available chlorine, the highest of all common pool sanitizers.
Question 2: What is the most effective disinfecting form of free chlorine in pool water?
- Hypochlorite ion (OCl⁻)
- Hypochlorous acid (HOCl) (Correct answer)
- Monochloramine (NH₂Cl)
- Dichloramine (NHCl₂)
Correct answer: Hypochlorous acid (HOCl)
Hypochlorous acid (HOCl) is the active, uncharged form of chlorine that penetrates cell walls and kills microorganisms most effectively.
Question 3: Trichlor and dichlor are considered 'stabilized' chlorines because they contain:
- Calcium carbonate
- Cyanuric acid (CYA) (Correct answer)
- Sodium bicarbonate
- Potassium monopersulfate
Correct answer: Cyanuric acid (CYA)
Stabilized chlorines contain cyanuric acid, which binds to chlorine and protects it from UV breakdown in sunlight.
Question 4: What effect does sodium hypochlorite (liquid chlorine) have on pool pH?
- Lowers pH significantly
- Has no effect on pH
- Raises pH due to its highly alkaline nature (Correct answer)
- Lowers total alkalinity only
Correct answer: Raises pH due to its highly alkaline nature
Sodium hypochlorite has a pH of 10–13, so adding it to pool water raises the pH over time.
Question 5: Which calcium-based chlorine product will gradually increase total calcium hardness in pool water?
- Trichlor tablets
- Sodium hypochlorite
- Calcium hypochlorite (cal hypo) (Correct answer)
- Sodium dichlor
Correct answer: Calcium hypochlorite (cal hypo)
Calcium hypochlorite releases calcium ions each time it dissolves, progressively raising calcium hardness levels.
Question 6: Why must calcium hypochlorite (cal hypo) and trichlor NEVER be mixed or stored together?
- They cancel each other's disinfection effect
- The combination can cause a violent fire or explosion (Correct answer)
- They produce excess cyanuric acid
- They lower pH to dangerous levels
Correct answer: The combination can cause a violent fire or explosion
Mixing cal hypo (oxidizer) with trichlor (acid) triggers a violent exothermic reaction that can cause fire, explosion, and toxic gas release.
Question 7: What is the recommended free chlorine range for a commercial swimming pool under the Model Aquatic Health Code?
- 0.1–0.5 ppm
- 1.0–5.0 ppm (Correct answer)
- 5.0–10.0 ppm
- 10.0–20.0 ppm
Correct answer: 1.0–5.0 ppm
The MAHC recommends maintaining free chlorine between 1.0 and 5.0 ppm in commercial pools to ensure effective disinfection.
CPO Disinfection and Sanitizers 2
Which chlorine product has the highest available chlorine content by percentage?