Figure 1-4. Percent of hypochlorous acid (molecular form) at varying pH.
c. Combined Available Chlorine. The chlorine oxidizes organic matter, such
as urine, and some inorganic substances. In this process, ammonia results and the
chlorine reacts with the ammonia to form compounds called chloramines. If this
process goes to completion, the ammonia is completely oxidized. If, however, there is
too much hypochlorous acid to complete the reaction, partially oxidized chloramines
remain in the water. This combination of chlorine and ammonia (chloramines) is called
combined available chlorine. Chloramines can kill bacteria, but 60 to 100 times slower
than free available chlorine. Combined available chlorine does not disperse as rapidly
as free available chlorine when exposed to sunlight or when water is agitated. Because
of this, some pool operators add ammonia on hot, sunny days. This, however, is not an
d. Total Chlorine. The amount of free available chlorine and combined
available chlorine is called total chlorine. When chloramines exist, water can be held to
bacteria-free standards by keeping the total chlorine at a concentration of 2.0 to 2.5
ppm (parts per million). This practice is undesirable, however, because chloramines
cause eye irritation and produce unpleasant chlorine odors.