Answer:

When this occurs the best course of action is to raise the chlorine level to around 20 ppm for at least 24 hours and allow the chlorine time to destroy any slow responding contaminants that can be present in loose stool. Then wait for the chlorine to come back down into the operating range, at least less than 10 ppm, before returning to swimming. The lower the chlorine level, the longer it takes to kill certain contaminants such as cryptosporidium.