Florida State Service and Repair Pool Contractor Practice Exam

To determine the correct amount of additional chlorine needed to eliminate the combined chlorine in a pool, it's essential to understand the typical ratio of chlorine required to break down combined chlorine (which primarily consists of chloramines). A common guideline suggests that it usually takes about 2.5 to 3 times the amount of combined chlorine present to effectively oxidize and eliminate chloramines.

In this scenario, with a combined chlorine reading of 0.4 ppm, applying the guideline suggests calculations might yield a requirement of around 1.0 to 1.2 ppm of free chlorine for breakdown. To ensure complete elimination, the recommendation shifts to add more chlorine, typically indicated to be around 4.0 ppm. This ensures that any persistent combined chlorine is effectively neutralized, resulting in improved overall water clarity and sanitation.

The total volume of the pool, which is 125,000 gallons, helps in contextualizing the amounts, but the critical factor lies in the chlorine ratio. Hence, the answer reflects appropriate practice in pool chemistry, targeting a 4.0 ppm addition of chlorine to completely address the combined chlorine issue.