Most often hot tub shock is an extra application of chlorine granules or liquid chlorine. The shock process accomplishes three important tasks: 1) it removes organic contaminants from the water, 2) it eradicates chloramines and bromines, and 3) it kills pathogens, bacteria, viruses, and algae (none of which make good soaking companions).

Why do hot tubs need to be shocked more often than pools? The size of hot tubs means that the water is affected more quickly by regular use than pools. The average hot tub might only hold 500 gallons of water, whereas the average swimming pool might hold 10,000 gallons of water. If you imagine five people using a hot tub and five people using a swimming pool — it’s pretty easy to see how water becomes dirty faster when there’s 100 gallons per person as opposed to 2,000 gallons per person.

Also, the “hot” in “hot tub” means the same products that are effective for shocking pools are not as effective for sanitizing hot tubs. Unstabilized chlorine (or calcium hypochlorite), for example, is rendered less effective by the heated water of a hot tub.

How often should I shock my hot tub? To keep your water clear and safe, Zagers recommends shocking your hot tub weekly. If you’re using your hot tub heavily (and good for you if you are), you may want to increase the frequency to more than once a week.