Also Known As: Combined Chlorine

Typically, too much chlorine is blamed for a strong-smelling pool. In actuality, it is likely caused by chloramines or combined chlorines, which are formed when free, available chlorine reacts with ammonia or other nitrogen-containing compounds.

When there is not enough free chlorine available to oxidize nitrogen-based compounds, like sweat, oils and urine, chloramines are formed. These are foul-smelling skin irritants with weaker disinfecting properties.

The solution is typically superchlorination or shock treatment. In this process a large amount of chlorine is added to the water to eradicate the excess organic matter and chloramines. Non-chlorine shocking agents include monopersulfate-based oxidizers, like potassium peroxymonosulfate. Still, chloramines can be challenging to get rid of. Weekly shock treatments may be necessary, with a more frequent schedule in pools that see a great deal of activity.

Preventative measures include requiring swimmers to shower with soap before getting in the water. In addition, when the temperature of the water is lower, swimmers sweat less, which reduces the ammonia in the water. And of course, swim diapers should be required for all children who are not toilet trained.

Chloramines can also be released into the air, which can be a particular problem in indoor pools and spas. Therefore, air filtration is a critical concern at these facilities. In addition, fresh air should circulate above the water.