NASCO Water Chemistry & Quality Control 4 — Questions and Answers
Question 1: What is the typical recommended turnover rate for a competition pool?
- Every 8 hours (Correct answer)
- Every 6 hours
- Every 4 hours
- Every 2 hours
Correct answer: Every 8 hours
A standard competition or general lap pool typically requires a complete water turnover every 8 hours (or 3 turnovers per day).
Question 2: Sodium carbonate (soda ash) is added to pool water primarily to:
- Lower pH
- Raise pH (Correct answer)
- Increase calcium hardness
- Increase cyanuric acid
Correct answer: Raise pH
Soda ash (sodium carbonate) is a strong base used to raise pH when it falls below the acceptable range of 7.2–7.8.
Question 3: Which pathogen is MOST resistant to normal chlorine levels and requires significantly higher contact time or UV/ozone treatment?
- E. coli O157:H7
- Giardia lamblia
- Cryptosporidium parvum (Correct answer)
- Pseudomonas aeruginosa
Correct answer: Cryptosporidium parvum
Cryptosporidium oocysts are extremely resistant to chlorine and typically require UV light or ozone for effective inactivation.
Question 4: What effect does high cyanuric acid (above 100 ppm) have on pool sanitation?
- It accelerates chlorine activity
- It over-stabilizes chlorine, reducing its germicidal effectiveness (Correct answer)
- It raises pH significantly
- It eliminates the need for shocking
Correct answer: It over-stabilizes chlorine, reducing its germicidal effectiveness
Excessive cyanuric acid binds chlorine so tightly that the chlorine becomes much less effective at killing pathogens — a condition called 'chlorine lock'.
Question 5: When testing pool water, samples should be collected from where?
- The surface skimmer
- At least 12–18 inches below the surface away from inlets (Correct answer)
- Directly from a return jet
- The deep end drain
Correct answer: At least 12–18 inches below the surface away from inlets
Water samples should be taken at elbow depth (12–18 inches below surface) away from inlets to get a representative reading of pool conditions.
Question 6: What is the function of a pool's recirculation system in relation to water chemistry?
- It adds chemicals automatically
- It distributes chemicals evenly and removes debris through filtration (Correct answer)
- It measures chlorine demand
- It controls water temperature only
Correct answer: It distributes chemicals evenly and removes debris through filtration
The recirculation system circulates water through the filter, ensuring even chemical distribution and removal of suspended particles and contaminants.
Question 7: Which chemical combination is DANGEROUS and must never be mixed together?
- Sodium bicarbonate and muriatic acid
- Calcium hypochlorite and trichlor (trichloroisocyanuric acid) (Correct answer)
- Soda ash and sodium bicarbonate
- Sodium bicarbonate and cyanuric acid
Correct answer: Calcium hypochlorite and trichlor (trichloroisocyanuric acid)
Mixing calcium hypochlorite with trichlor can cause violent chemical reactions, fires, or explosions due to their incompatible chemistry.
NASCO Water Chemistry & Quality Control 4
What is the typical recommended turnover rate for a competition pool?