Water Chemistry & Testing Procedures Flashcards

At what Combined Chlorine (CC) level should breakpoint chlorination be performed?

Answer: 0.3 ppm or above

When combined chlorine reaches 0.3 ppm or above, breakpoint chlorination should be performed to destroy chloramines and restore water quality.

How much free chlorine is needed to achieve breakpoint chlorination when combined chlorine is 0.5 ppm?

Answer: 4.0 ppm additional free chlorine

Breakpoint chlorination requires adding free chlorine to a level 10 times the combined chlorine; 0.5 ppm CC × 10 = 5.0 ppm, so approximately 4.0–5.0 ppm of additional free chlorine is needed above existing levels.

A test kit measures Total Chlorine at 3.0 ppm and Free Chlorine at 2.2 ppm. What is the Combined Chlorine level?

Answer: 0.8 ppm

Combined Chlorine = Total Chlorine − Free Chlorine; 3.0 − 2.2 = 0.8 ppm.

Which of the following BEST describes the role of Total Alkalinity in pool water chemistry?

Answer: It acts as a pH buffer, resisting rapid pH changes

Total Alkalinity is the measure of water's buffering capacity, preventing large swings in pH when acids or bases are added.

Sodium carbonate (soda ash) is added to pool water primarily to:

Answer: Raise both pH and Total Alkalinity

Soda ash (sodium carbonate) raises pH significantly and also increases Total Alkalinity, making it the preferred chemical for correcting low pH.

What effect does high CYA (above 90 ppm) have on pool sanitation?

Answer: It reduces the percentage of active hypochlorous acid (HOCl)

High CYA levels bind chlorine molecules, dramatically reducing the fraction of active HOCl available to kill pathogens—a phenomenon called 'chlorine lock.'

A colorimetric test kit result for pH shows a color between two printed standards. The operator should:

Answer: Interpolate between the two standards for the best estimate

When a color falls between two standards, the operator should estimate by interpolating between the two values to achieve the most accurate reading.