For a 32,000-gallon pool with a total chlorine of 2.4 ppm and a free chlorine of 1.3 ppm, how much combined chlorine must be added to achieve breakpoint chlorination?

To achieve breakpoint chlorination, it's essential to understand the relationship between total chlorine, free chlorine, and combined chlorine. Breakpoint chlorination occurs when enough chlorine is added to convert all combined chlorine (chloramines) into free chlorine, thereby eliminating the smell and irritation typically associated with chloramines.

In this case, the total chlorine is 2.4 ppm, and the free chlorine is 1.3 ppm. The combined chlorine can be calculated by subtracting the free chlorine from the total chlorine:

Combined chlorine = Total chlorine - Free chlorine

Combined chlorine = 2.4 ppm - 1.3 ppm = 1.1 ppm

To determine how much chlorine must be added to achieve breakpoint chlorination, it's necessary to add enough chlorine to exceed the concentration of combined chlorine in the pool. This typically means adding a dose of chlorine that is at least twice the amount of the combined chlorine present.

Given that the combined chlorine is 1.1 ppm, you should aim to add at least 1.1 ppm of chlorine to break it down, but usually, a bit more is recommended—typically about twice the initial combined chlorine. This leads to a total requirement that typically exceeds this amount to ensure a complete reaction and purification.

Therefore