CPO Disinfection and Sanitizers 3

Question 1

At a pool pH of 7.5, approximately what percentage of free chlorine exists as the effective hypochlorous acid (HOCl) form?

Accepted Answer

About 50%

Answer

At pH 7.5, the equilibrium between HOCl and OCl⁻ is approximately 50/50, making pH 7.5 a balance point for disinfection efficiency.

Question 2

Why is cyanuric acid (CYA) added to outdoor pools?

Accepted Answer

To protect chlorine from ultraviolet (UV) sunlight degradation

Answer

CYA bonds to free chlorine, shielding it from UV radiation and extending its useful life in outdoor pools.

Question 3

What is the generally accepted maximum recommended level of cyanuric acid in a swimming pool?

Accepted Answer

100 ppm

Answer

Above 100 ppm, cyanuric acid over-stabilizes chlorine, significantly reducing its disinfection effectiveness (chlorine lock).

Question 4

What is the only reliable way to reduce excessively high cyanuric acid levels in a pool?

Accepted Answer

Partially drain and refill with fresh water

Answer

CYA does not degrade or filter out; diluting the water by partial drain-and-refill is the only practical way to lower it.

Question 5

When pool pH drops below 7.2, what is the primary operational concern?

Accepted Answer

Corrosion of equipment, surfaces, and swimmer discomfort

Answer

Low pH (acidic conditions) corrodes metal fittings, etches plaster, degrades gaskets, and causes eye/skin irritation.

CPO (Certified Pool Operator Exam) Practice Test