Water Chemistry & Testing Procedures Flashcards

What is the recommended testing frequency for free chlorine and pH in a public pool under heavy bather load?

Answer: Every 4 hours minimum, or more frequently during heavy use

Health codes typically require testing free chlorine and pH at least every 4 hours in public pools, with more frequent testing during peak bather loads.

Sodium bicarbonate is preferred over soda ash to raise Total Alkalinity because:

Answer: It raises alkalinity with a smaller increase in pH

Sodium bicarbonate raises Total Alkalinity effectively while causing only a modest pH increase, making it easier to adjust alkalinity without overshooting target pH.

A pool operator suspects algae growth. Which water chemistry condition would MOST likely contribute to this problem?

Answer: Free chlorine of 0.2 ppm and pH of 8.2

Very low free chlorine (0.2 ppm) combined with high pH (8.2) dramatically reduces the percentage of active HOCl, creating ideal conditions for algae growth.

Total Dissolved Solids (TDS) in pool water should be monitored because excessively high TDS can:

Answer: Reduce water clarity, interfere with chemical balance, and cause a salty taste

High TDS (typically above 1,500 ppm above fill water baseline) can cause cloudy water, chemical interference, and a salty or bitter taste, often necessitating partial draining and refilling.

When should a pool operator calibrate an electronic ORP/pH controller?

Answer: At installation and then monthly or per manufacturer recommendation

Electronic controllers require regular calibration—typically monthly or per the manufacturer's schedule—using buffer solutions to ensure accurate pH and ORP readings.

A pool operator adds cal-hypo (calcium hypochlorite) shock to the water. This will ALSO cause which secondary water chemistry change?

Answer: An increase in calcium hardness

Calcium hypochlorite contains calcium, so repeated use will gradually raise the pool's calcium hardness level, which must be monitored to avoid scale formation.

Which condition would cause a DPD chlorine test to produce an artificially LOW free chlorine reading?

Answer: High copper levels in the water (above 0.3 ppm)

Copper and other metals can interfere with DPD test reagents, causing oxidation of the indicator and producing falsely low or unreliable chlorine readings.