Hot Tub Shock is used to oxidize and remove unwanted oils and bacteria from spa water. Mostly a weekly treatment, shock is used whenever the water is cloudy from heavy use or when the chlorine-bromine levels get too low. Chlorine based and Chlorine free shock is available in multiple sizes for treatment of your spa water. Non Chlorine Shock also is known as MPS or mono per sulfate. Pool Geek carries many sizes and brands of the Spa Shock, our most purchases spa chemical.