Breakpoint Chlorination

 

FAC = Free Active Chlorine ---------------- Active & Useful Chlorine
CAC = Combined Active Chlorine --------- Chloramines / Ineffective Chlorine
TAC = Total Available Chlorine ------------ Sum of FAC and CAC

Chloramines are the largest single problem in pool water maintenance.  Chloramines have about 2% of the germ killing power compared to FAC.  They are the source of eye irritation in swimmers, not to mention the obnoxious “chlorine smell” complaint so often encountered.

The standard method for removal of chloramines is by breakpoint chlorination.  Breakpoint is achieved by introducing 10 times the CAC level in the form of new chlorine or shock. 

TAC = FAC + CAC
CAC = TAC - FAC

 

An Example of Breakpoint Chlorination:
Assume the pH is between 7.4 and 7.6.
Assume TAC = 2.0 ppm
Assume FAC = 0.5 ppm
Then CAC = 1.5 ppm x 10 = 15 ppm

Therefore, add 15 ppm of new chlorine or shock to the pool water to achieve breakpoint chlorination.  Do not allow swimmers back into the pool until the chlorine level drops to 4 ppm or less.

Sure Shock ----------------- 1 lb. in 10,000 gallons will raise the water 5 ppm
Non-Chlorine Shock -------- Not recommended for breakpoint chlorination
Multi-Shock ----------------- 1 lb. in 10,000 gallons will raise the water 3 ppm
Fast Shock ------------------ 1 lb. in 10,000 gallons will raise the water 2.5 ppm

We do not recommend using a “stabilized” chlorine for achieving breakpoint chlorination. It can cause the stabilizer level (cynauric acid) to increase to a higher than recommended level. The only way to lower stabilizer in a pool is to drain water. Triclor (tablets and sticks) and dichlor (granular) are examples of stabilized chlorine.