Long Answer: Not all of you ...
Published by Daniel Couton, Process and Environmental Chemist
Long Answer: Not all of you ammonia will necessarily be present as monochloramine. A while back I was involved in a large study that was tracking monochloramine along a 800km (500 mile) pipeline. At the beginning of the process the total ammonia and total chlorine agreed with each other, however, as time passed they started to fall further and further apart indicating that the monochloramine system was failing.
Short Answer: It is a good check to do to confirm that your system is operating as expected.