What is Free Chlorine?

Chlorine (or bromine) is used in pools and spas as a means of sanitizing the water and ensure that it can be considered safe for swimmer or bather use. It can be measured as either Total Chlorine (all of the chorine in the water) and Free Chlorine (what is actively free and available to fight off bacteria, contaminants, and other health concerns).

Typically, Free Chlorine is the common regular test performed; but Total Chlorine readings -- when greater than the tested Free Chlorine -- can directly indicate that nitrogen and other contaminants are in play and preventing the chlorine from effectively doing its primary job.

Usually, such conditions can also be physically identified by a foul "chlorine" odor or excessive eye irritation when using the pool or spa.