Combined chlorine (chloramines)
The portion of chlorine in your water that has already reacted with contaminants and lost most of its sanitizing power, better known as chloramines.
Combined chlorine, or chloramines, forms when free chlorine reacts with ammonia and nitrogen compounds from sweat, urine, and other organic material, binding into a weaker compound that's mostly used up. It's the actual source of that sharp 'chlorine smell' most people associate with too much chlorine, when in fact it usually means there isn't enough free chlorine relative to the contaminant load. Healthy pools keep combined chlorine at or near 0 ppm, and no higher than about 0.5 ppm; anything above that is a signal to superchlorinate and reach breakpoint chlorination rather than to add a small routine dose.
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