How To Shock a Pool

The "smell of chlorine" in a pool is actually the smell of chloramines, the chemical compounds formed when chlorine combines with sweat, oils, urine and other contaminants in the water. Chloramines are not effective in disinfecting the water and cause eye and skin irritation.  Breakpoint Superchlorination or "Pool Shocking" is required to combat the loss of effective chlorine in the water.  Breakpoint Superchlorination is required (on average) every 2-3 weeks for indoor pools and every 7-10 days for outdoor pools.  Heavy bather loads will increase the need for Breakpoint Superchlorination.  Instructions for Breakpoint Superchlorination of your water are available to read below, or you can download and print a copy of the instructions in Adobe PDF format.

Increasing or Decreasing Chlorine Levels

The chloramine level is calculated by subtracting the free chlorine from the total chlorine in the pool/spa water. Pool/spa water must be tested for combined level at least twice a week. Although most courses recommend the level not to exceed .2 ppm, we recommend that the level not exceed .5 ppm (due to the availability of reasonably priced test kits). The average frequency of shocking is 2-3 weeks for an indoor pool and 7-10 days for an outdoor pool. However, high bather loads will result in more frequent superchlorination.  NOTE: Pools using bromine as a sanitizer must also perform breakpoint superchlorination using chlorine, as bromine is not available in a form for this procedure. (bromine for pools is a compound of bromine and chlorine) Like chlorine, bromine combines with organic impurities to form combined bromine and bromamines.

Shocking the Pool

1. Determine the ppm of free available chlorine (FAC)

2. Determine the ppm of total available chlorine (TAC)

3. Determine the ppm of combined available chlorine (CAC) or chloramines using this formula:
   TAC - FAC = CAC
   For Example:
   TAC (2.0 ppm) - FAC (1.5 ppm) = 0.5 ppm (CAC) or
   TAC (3.0 ppm) - FAC (2.0 ppm) = 1.0 ppm (CAC)

   Steps 1-3 must be done using a DPD test, using the test kit instructions.

4. Determine the breakpoint factor using this formula:
   (CAC) x (10) = breakpoint factor (in ppm)

   This is the level, in ppm, of chlorine needed to reach "breakpoint"

5. Identify the type of chlorine to be used for "shocking"
   
   Stabilized chlorine compounds, such as Sodium Dichlor Granular Chlorine or Sodium Trichlor Granular Chlorine may not be used for "shocking" because the permitted level of cyanuric acid would be exceeded over the season. It also would cause the water to have elevated chlorine levels for days.
    

6. Plug the breakpoint factor into the right formula:

   • Calcium Hypochlorite
     (0.125) x (breakpoint factor) x (pool volume / 10,000) = pounds to add

   • Lithium Hypochlorite
     (0.250) x (breakpoint factor) x (pool volume / 10,000) = pounds to add

   • Sodium Hypochlorite
     (0.1016) x (breakpoint factor) x (pool volume / 10,000) = gallons to add
     
     Note "/" means divided by.

     For Example:
     Calcium Hypochlorite will be used, CAC is .5, therefore the breakpoint factor is 5 (CAC x 10), the pool volume is 100,000 gallons.
     (0.125) x (5) x (100,000 / 10,000) = 6.25 pounds of calcium hypochlorite must be added to the pool.

Non-Chlorine Oxidizers
Non-chlorine oxidizers may be used to "shock" a pool, but the pool will still have to be superchlorinated periodically with a chlorine compound to kill off the bacteria that become resistant to constant exposure to low levels of disinfectant (chlorine and bromine). An advantage to using a non-chlorine oxidizer is the shut down may be as little as one half-hour. These products will oxidize or destroy ammonia, nitrogen and some swimmer waste, but will not kill bacteria or algae. The active ingredient used in non-chlorine oxidizers is Potassium monopersulfate

Note that the use of potassium monopersulfate will result in false readings of chlorine for up to 6 hours as it oxidizes the iodide in the reagent as if it were combined chlorine. There is a reagent available to correct this.