CPO Pool Calculations and Formulas 3 — Questions and Answers
Question 1: The standard weight of water used in pool chemical dosage calculations is:
- 7.48 lbs per gallon
- 8.34 lbs per gallon (Correct answer)
- 6.25 lbs per gallon
- 10.0 lbs per gallon
Correct answer: 8.34 lbs per gallon
Water weighs 8.34 lbs per gallon, which is the standard value used when calculating parts per million in pool water.
Question 2: Using the formula: lbs = (ppm × gallons × 8.34) / (% × 10,000), how many pounds of calcium hypochlorite (65% available chlorine) are needed to raise a 10,000-gallon pool by 2 ppm?
- 0.13 lbs
- 0.26 lbs (Correct answer)
- 0.52 lbs
- 1.02 lbs
Correct answer: 0.26 lbs
lbs = (2 × 10,000 × 8.34) / (65 × 10,000) = 166,800 / 650,000 ≈ 0.26 lbs of cal hypo.
Question 3: A pool has combined chlorine (chloramines) measuring 0.5 ppm. To achieve breakpoint chlorination, the free chlorine level must reach at least:
- 0.5 ppm
- 2.5 ppm
- 5.0 ppm (Correct answer)
- 10.0 ppm
Correct answer: 5.0 ppm
Breakpoint chlorination requires free chlorine to reach 10 times the combined chlorine level: 10 × 0.5 = 5.0 ppm.
Question 4: Which chemical is typically used to LOWER pH in a swimming pool?
- Sodium carbonate (soda ash)
- Sodium bicarbonate (baking soda)
- Muriatic acid (hydrochloric acid) (Correct answer)
- Calcium hypochlorite
Correct answer: Muriatic acid (hydrochloric acid)
Muriatic acid (HCl) or dry acid (sodium bisulfate) is used to lower pH because both are acidic compounds.
Question 5: Sodium hypochlorite solution at 12.5% strength weighs 10.0 lbs per gallon. How many ounces of actual (available) chlorine are in 1 gallon?
- 2 oz
- 12.5 oz
- 20 oz (Correct answer)
- 25 oz
Correct answer: 20 oz
12.5% of 10.0 lbs = 1.25 lbs of available chlorine × 16 oz/lb = 20 oz of available chlorine per gallon.
Question 6: When adding sodium carbonate (soda ash) to raise pH, which secondary effect must the operator monitor?
- It lowers calcium hardness
- It also raises total alkalinity (Correct answer)
- It reduces cyanuric acid concentration
- It increases TDS without affecting alkalinity
Correct answer: It also raises total alkalinity
Soda ash raises both pH and total alkalinity simultaneously, so alkalinity must be monitored to avoid it exceeding 120 ppm.
Question 7: A 20,000-gallon pool needs its free chlorine raised from 0 to 3 ppm using calcium hypochlorite (65% available Cl). Using the formula lbs = (ppm × gallons × 8.34) / (% × 10,000), approximately how many pounds are needed?
- 0.39 lbs
- 0.77 lbs (Correct answer)
- 1.54 lbs
- 3.08 lbs
Correct answer: 0.77 lbs
lbs = (3 × 20,000 × 8.34) / (65 × 10,000) = 500,400 / 650,000 ≈ 0.77 lbs of calcium hypochlorite.
CPO Pool Calculations and Formulas 3
The standard weight of water used in pool chemical dosage calculations is: