Terminology
In the industry, there are a number of terms used to
indicate the various forms of chlorine that are of
interest. These terms tend to be used rather loosely
and not necessarily consistently. For that reason,
the following terms are defined:
Free Available Chlorine refers to the
hypochlorous acid (HOCl) form of chlorine only.
It is the free, uncombined form of chlorine that is
effective for disinfection.
Total Free Chlorine refers to the sum of
hypochlorous acid (HOCl) and hypochlorite ion