Do you have too much chlorine in the pool?
Perhaps you are swimming in a heavily used pool; or maybe you are in the bleachers at the natatorium watching the big swim meet. You notice the smell of “chlorine” in the air. And – it’s bad – really bad. If you are in the pool, your eyes may be stinging and swelling. Even if you are up in the bleachers, you realize that your eyes are becoming red and irritated. Either place, you smell “the smell.” “Too much chlorine, again!” you think. “I told them last week that they were using too much chlorine, and they obviously weren’t listening.” You resolve to go talk to the pool manager again, and make sure that she hears you – loud and clear – this time.
You find the pool manager in her office, and you begin reading her the riot act. Fortunately, she is a patient person, and lets you say your piece. Her response, though, is not what you expected.
She explains to you that the smell, eyeburn, and irritation weren’t a result of having too much chlorine in the pool water, but from not having enough! And she tells you why:
Swimmers’ sweat and other organic pool water contaminants contain nitrogen-rich ammonia. As long as the pool water maintains at least ten times as much molecular weight of chlorine than nitrogen, the nitrogen off-gasses to the atmosphere. Outdoors, it blows away; indoors, it must be evacuated from the natatorium (and it usually doesn’t get all evacuated, which leads to big problems). But if there is less that ten times as much chlorine in the water than the nitrogen being introduced, then the nitrogen combines with the chlorine, making chloramine.
A pool can be “heavily” chlorinated (20 ppm+) and, as long as there are no chloramines, the water will not have “the smell” and it will not cause irritation. But just a little bit of chloramine (0.4 ppm and higher) leads to eyeburn, irritation, “the smell”, and contributes to respiratory damage. Chloramines are created when the chlorine residual in the pool water is lower than what is required to treat the nitrogen load. Chloramines can be destroyed by adding enough chlorine to the water to overcome the molecular weight imbalance and restore the 10:1 chlorine/nitrogen ratio.
“So” the pool manger says “I need to do some water testing when the pool closes, and calculate how much chlorine I need to add to destroy the chloramines. I will multiply my chloramine level by ten, then add this much chlorine directly to the water. I’m going to add it tonight, and the pool will be closed tomorrow until the chloramines are gone and the free chlorine residual drops to an acceptable level.”
You ponder this as you drive home: The red eyes, irritation, and smell are not caused by too much chlorine, but from actually having too little chlorine during a high organic load. And – even stranger – more chlorine, in the right amount, needs to be added to the pool water to get rid of the smell and other problems.