According to the Certified Pool - Spa Operator Handbook, which scenario should result in the immediate closure of a pool or spa?

The scenario that should lead to the immediate closure of a pool or spa is when the water temperature exceeds 104°F. This high temperature can pose significant health risks, particularly for vulnerable populations such as young children, the elderly, and individuals with certain medical conditions. At temperatures above 104°F, individuals may experience heat-related illnesses like heat exhaustion or heat stroke, as well as impaired judgment and motor skills.

It's critical for pool operators to monitor the temperature regularly and ensure that it remains within safe limits, as exceeding this threshold can put patrons' health in jeopardy and lead to serious consequences. This is why the immediate closure of the facility is necessary in such instances to protect public health and safety.

Other scenarios, such as a pH level reading of 8.0 or a chlorine level below 1 ppm, indicate issues that may require attention or remediation, but they do not provide an immediate health hazard that warrants shutting down the facility. Similarly, the presence of algae should prompt action to clean and treat the water, but it does not represent an immediate health threat to swimmers at that moment.