Case Analysis & Practical Application Flashcards

A CPO is evaluating water test results for a heated indoor pool: pH 7.6, FC 2 ppm, TA 100 ppm, CH 250 ppm, water temp 84°F. What does the LSI calculation suggest?

Answer: The water is balanced and within acceptable range

These parameters (pH 7.6, TA 100, CH 250, temp 84°F) typically yield an LSI near 0, indicating balanced water within the acceptable range of −0.3 to +0.3.

A pool operator adds 20 lbs of calcium hypochlorite (65%) to a 100,000-gallon pool for superchlorination. What approximate free chlorine increase should be expected?

Answer: 10 ppm

Calcium hypochlorite at 65% has an available chlorine factor where approximately 1 lb raises a 10,000-gallon pool about 7 ppm; 20 lbs in 100,000 gallons ≈ 10 ppm increase.

A CPO suspects Cryptosporidium contamination following a diarrheal fecal incident. After removing visible matter, what minimum chlorine concentration and contact time does the CDC recommend for inactivation?

Answer: 20 ppm for 12.75 hours at pH 7.5

Cryptosporidium is highly chlorine-resistant; CDC recommends raising FC to 20 ppm and maintaining for approximately 12.75 hours (CT value of 15,300) at pH 7.5 and 77°F.

An outdoor pool's total dissolved solids (TDS) reading is 3,200 ppm, up from a baseline of 400 ppm at the start of the season. What is the most practical corrective action?

Answer: Partially drain and refill the pool to dilute TDS

High TDS cannot be reduced chemically; partial drain and refill is the standard method to dilute accumulated dissolved solids to an acceptable level (typically below 1,500–2,000 ppm above the fill water baseline).

A CPO finds that a pool's heater heat exchanger has calcium scale buildup reducing efficiency. Which water chemistry factor MOST directly caused this problem?

Answer: Calcium hardness and alkalinity resulting in a positive LSI

Scale on heat exchangers results from oversaturated water with high calcium hardness and alkalinity creating a positive LSI, causing calcium carbonate to precipitate on hot surfaces.

A CPO notices that the pool pump is running but water flow appears reduced and the pump sounds unusual. The pressure gauge reads 5 psi below normal operating pressure. What is the MOST likely cause?

Answer: Air leak or obstruction on the suction side of the pump

Lower-than-normal pressure with reduced flow and unusual pump sounds indicates a suction-side air leak or blockage, causing the pump to cavitate or draw air instead of water.

A facility manager asks the CPO why the chlorine demand seems very high even though bather load is low. The pool is outdoors with no stabilizer. What is the MOST likely explanation?

Answer: UV radiation from sunlight is rapidly destroying unstabilized chlorine

In outdoor pools without cyanuric acid (stabilizer), UV rays from the sun can destroy up to 90% of free chlorine within a few hours, explaining high apparent chlorine demand.