CPI Water Quality & Treatment Standards 3 — Questions and Answers
Question 1: What is the Langelier Saturation Index (LSI) used to predict in pool water?
- Chlorine demand based on bather load
- Whether water will be scale-forming or corrosive (Correct answer)
- The rate of cyanuric acid breakdown
- Filter media replacement intervals
Correct answer: Whether water will be scale-forming or corrosive
The LSI predicts whether water is balanced — a positive value indicates scale-forming tendency; a negative value indicates corrosive tendency.
Question 2: At what pH level does hypochlorous acid (the active sanitizing form of chlorine) exist in its highest concentration?
- 6.0–6.5
- 7.2–7.4 (Correct answer)
- 7.8–8.0
- 8.5–9.0
Correct answer: 7.2–7.4
At pH 7.2–7.4, approximately 75–80% of chlorine exists as hypochlorous acid, the most effective sanitizing form.
Question 3: A spa inspector measures the water temperature at 104°F. What is the primary water quality concern at this temperature?
- Cyanuric acid precipitates out of solution
- Chlorine dissipates much faster requiring more frequent dosing (Correct answer)
- Total alkalinity drops below safe levels
- Salt chlorinators stop functioning
Correct answer: Chlorine dissipates much faster requiring more frequent dosing
Elevated spa temperatures dramatically accelerate chlorine dissipation, requiring more frequent monitoring and dosing to maintain safe sanitizer levels.
Question 4: What does a 'total dissolved solids' (TDS) reading above 1,500 ppm above the source water baseline typically indicate?
- The pool needs shock treatment immediately
- Water needs to be partially drained and replaced (Correct answer)
- pH adjusters are no longer effective
- The filter is bypassing water
Correct answer: Water needs to be partially drained and replaced
High TDS (>1,500 ppm above fill water) means dissolved minerals and chemicals have accumulated to a level requiring partial drain and refill.
Question 5: Which type of algae is hardest to treat and typically requires brushing plus a specialized algaecide or high-dose chlorine shock?
- Green algae
- Yellow/mustard algae
- Black algae (Correct answer)
- Pink algae (actually a bacteria)
Correct answer: Black algae
Black algae embeds its roots into plaster and grout, making it very difficult to eradicate and requiring aggressive brushing and high chlorine levels.
Question 6: When using sodium dichloro-s-triazinetriene (dichlor) as a sanitizer, what secondary effect must inspectors be aware of?
- It raises pH significantly
- It increases cyanuric acid levels with each application (Correct answer)
- It causes calcium hardness to drop rapidly
- It destroys phosphates in the water
Correct answer: It increases cyanuric acid levels with each application
Dichlor is a stabilized chlorine product; repeated use steadily increases cyanuric acid levels, which can eventually impair chlorine effectiveness.
Question 7: What is the purpose of a 'phosphate remover' product in pool water treatment?
- Neutralize chloramines directly
- Remove algae nutrients that promote algae growth (Correct answer)
- Lower total alkalinity quickly
- Increase free chlorine residual
Correct answer: Remove algae nutrients that promote algae growth
Phosphates are a primary nutrient source for algae; removing them helps prevent algae blooms and reduces chlorine demand.
CPI Water Quality & Treatment Standards 3
What is the Langelier Saturation Index (LSI) used to predict in pool water?