Breakpoint Chlorination

Combined chlorine (C.C.) is free available chlorine that has combined with wastes containing nitrogen or ammonia (also known as chloramines). Combined chlorine will cause a noticeable "chlorine odour" and can cause skin, eye, and mucous membrane irritation. It also has little disinfecting power. Breakpoint chlorination is used to get rid of combined chlorine.

To determine the amount of combined chlorine use the following equation:

Combined Chlorine = Total Chlorine - Free Available Chlorine

Breakpoint chlorination is a technique used to remove combined chlorine by adding free available chlorine. To reach breakpoint, sufficient chlorine must be added to the pool to raise the free available chlorine level to 10 times the amount of combined chlorine.

To determine the amount of chlorine that is required to achieve breakpoint, use the following equation:

# of ozs, qrts, gallons, mLs, L, etc = [ppm required] x [amount of water]/1 000 000 x [% Chlorine/ 100]

Example: An 80, 000 L pool has 2 ppm free available chlorine, and 5 ppm total chlorine. Liquid chlorine at 5% is used to shock the pool.

Step 1 : Combined Chlorine = Total Chlorine - Free Available Chlorine

C.C. = 5 ppm - 2 ppm

=3 ppm of combined chlorine

Step 2 : 10 x 3ppm = 30

Therefore the FAC residual in the pool must be raised to 30 ppm.

Step 3 :

Volume required to raise the pool by 30 ppm = [ppm required] x [amount of water]/1 000 000 x [% Chlorine/ 100]

= [30 ppm] x [80 000 L]/1 000 000 x [%5/100]

= 48 L

Therefore 48 L is required to be added to the pool.

Revised: 2011-11-15