Pool Shock Dosage Calculator

When and why pools get shocked

Shocking (superchlorination) means adding a large dose of chlorine all at once, well beyond normal daily maintenance levels - typically done to break down chloramines, kill algae blooms, or recover clarity after heavy bather load, a storm, or contamination.

Worked example

For a 20,000-gallon pool targeting a 10 ppm free chlorine increase:

Dose = (20000/10000) x (10/10) = 2.0 lbs cal-hypo shock

Frequently asked questions

When should shock be added? Always add shock at dusk or after dark - direct sunlight rapidly burns off the chlorine boost through UV exposure, undermining the entire purpose of the treatment before it can do its job.

Is swimming safe right after shocking? No - wait until free chlorine drops back to a normal range (typically 1-4 ppm) before swimming, which can take anywhere from a few hours to overnight depending on shock strength and pool conditions.