Pool Fouling Guidelines

Diarrhea in Water when Chlorine Stabilizer is NOT in the Water

A diarrheal incident is a high-risk event for contamination caused by Cryptosporidium (Crypto), an extremely chlorine-tolerant parasite. It is important that aquatic staff educate users not to swim when ill with diarrhea. To disinfect the water following a diarrheal incident, staff should hyperchlorinate, or raise the free chlorine concentration to a high concentration for a long period of time. If needed, before attempting to hyperchlorinate, consult an aquatic professional to determine the possibility, most optimal or practical methods and safety considerations.

Step 1: Close the aquatic venue to swimmers. If you have multiple venues that use the same filtration system, all venues will have to be closed. Do not allow anyone to enter the venue(s) until the hyperchlorination process is completed.
Step 2: Remove as much of the fecal matter as possible (using a net or bucket) and dispose of the fecal matter in a sanitary matter. Clean and disinfect the item used to remove the fecal matter (after cleaning, leave the net or bucket immersed in water during hyperchlorination). Vacuuming fecal matter from the water is not recommended.
Step 3: Using unstabilized chlorine (sodium hypochlorite), raise the water's free chlorine concentration (see Table below) and maintain water at pH 7.5 or less.
Step 4: Achieve a concentration x time (CT) inactivation value of 15,300 to inactivate or kill Crypto. The CT inactivation value refers to the concentration of free chlorine in parts per million (ppm) multiplied by the time in minutes at a specific pH and temperature.
Step 5: Confirm the filtration system is operating while the water reaches and is maintained at the proper free chlorine concentration and pH for hyperchlorination.
Step 6: Backwash the filter thoroughly after reaching the CT inactivation value. Be sure to discharge directly to waste and according to state or local regulations. Do not return the backwash through the filter. Where appropriate, replace the filter media.
Step 7: Allow swimmers back into the water only after the required CT inactivation value has been achieved and the free chlorine concentration and pH are within the operating range.

Use the formula below to calculate the time required to inactivate or kill Crypto

Concentration x time (CT) inactivation value Divided by Free chlorine concentration
(parts per million [ppm])
Time (in minutes)
15,300 Divided by 20 = 765
(or 12.75 hours)
15,300 Divided by 10 = 1,530
(or 25.5 hours)

Diarrhea in Water when Chlorine Stabilizer IS in the Water

A diarrheal incident is a high-risk event for contamination caused by Cryptosporidium (Crypto), an extremely chlorine-tolerant parasite. It is important that aquatic staff educate users not to swim when ill with diarrhea. To disinfect the water following a diarrheal incident, staff should hyperchlorinate, or raise the free chlorine concentration to a high concentration for a long period of time. If needed, before attempting to hyperchlorinate, consult an aquatic professional to determine the possibility, most optimal or practical methods and safety considerations.

Step 1: Close the aquatic venue to swimmers. If you have multiple venues that use the same filtration system, all venues will have to be closed. Do not allow anyone to enter the venue(s) until the hyperchlorination process is completed.
Step 2: Remove as much of the fecal matter as possible (using a net or bucket) and dispose of the fecal matter in a sanitary matter. Clean and disinfect the item used to remove the fecal matter (after cleaning, leave the net or bucket immersed in water during hyperchlorination). Vacuuming fecal matter from the water is not recommended.
Step 3: Using unstabilized chlorine (sodium hypochlorite), raise the water's free chlorine concentration and maintain water at pH 7.5 or less.
Step 4:

Hyperchlorinate. Chlorine stabilizer slows the rate at which free chlorine inactivates or kills Crypto, and the more stabilizer there is in the water the longer it takes to kil Crypto. If the cyanuric acid concentration is 1-15 parts per million (ppm):

  • Raise the free chlorine concentration to 20 ppm for 28 hours or,
  • Raise the free chlorine concentration to 30 ppm for 18 hours or,
  • Raise the free chlorine concentration to 40 ppm for 8.5 hours

If the cyanuric acid concentration is more than 15 ppm, lower the concentration to 1-15 ppm by draining partially and adding fresh water without chlorine stabilizer before attempting to hyperchlorinate.

Step 5: Confirm the filtration system is operating while the water reaches and is maintained at the proper free chlorine concentration and pH for hyperchlorination.
Step 6: Backwash the filter thoroughly after reaching the CT inactivation value. Be sure to discharge directly to waste and according to state or local regulations. Do not return the backwash through the filter. Where appropriate, replace the filter media.
Step 7: Allow swimmers back into the water only after the required CT inactivation value has been achieved and the free chlorine concentration and pH are within the operating range.
Page Feedback Did you find what you were looking for today?