Water Chemistry & Testing Procedures Flashcards

What is the primary reason pool operators measure Oxidation Reduction Potential (ORP)?

Answer: To assess the water's overall sanitizing power regardless of chlorine form

ORP measures the water's oxidizing capacity (sanitizing power) in millivolts, which reflects the actual ability to destroy pathogens—accounting for pH, temperature, and chlorine form.

A pool's calcium hardness is 50 ppm. Which problem is MOST likely to occur?

Answer: Corrosion and etching of plaster, grout, and metal equipment

Low calcium hardness (below 150 ppm) makes water aggressive—it will leach calcium from plaster, grout, and metal fittings, causing corrosion and surface damage.

When adding muriatic acid to a pool, the operator should:

Answer: Pre-dilute acid in a bucket of pool water and add slowly near a return jet

Acid should be pre-diluted in a bucket of pool water (never water into acid) and added near a return jet with the pump running to ensure rapid, safe dispersion.

A spa test shows free chlorine at 5 ppm, pH 7.2, and CYA at 0 ppm. The water is BEST described as:

Answer: Potentially corrosive but highly sanitizing

At pH 7.2 and zero CYA, nearly all chlorine exists as the highly active HOCl form, providing excellent sanitation but also making the water slightly acidic and potentially corrosive over time.

Which component of the Langelier Saturation Index is NOT a factor in its calculation?

Answer: Cyanuric acid level

The LSI uses pH, temperature, calcium hardness, total alkalinity, and TDS—Cyanuric Acid is not a direct factor in the standard Langelier formula.

A new pool operator finds the water has a strong chlorine smell but swimmers complain of eye irritation. The MOST likely cause is:

Answer: Combined chlorine (chloramines) is elevated

The characteristic 'chlorine smell' and eye irritation are caused by chloramines (combined chlorine), not free chlorine—breakpoint chlorination is the solution.

Which test method is MOST accurate for measuring free chlorine levels above 5 ppm?

Answer: FAS-DPD (ferrous ammonium sulfate) titration test

The FAS-DPD titration test is accurate across a wide range of chlorine levels, including above 5 ppm, where standard DPD colorimetric tests 'bleach out' and give false low readings.