Why Do I Need Swimming Pool Shock?
Swimming pool shock is used to rid the water of organic compounds (specifically chloramines or combined chlorine) that tie up chlorine and prevent it from working effectively as a sanitizer. It’s the high levels of chloramines in the water that irritate swimmers and generate unpleasant odors. When swimmers complain of “too much chlorine in the water” that is irritating their eyes and nose. the problem is in fact too little free chlorine, not too much.
Shock treating your pool ensures that there is enough freely available chlorine to keep bacteria, algae and pathogens at bay and disinfect any contaminants ensuring the water remains clear and safe for swimmers. Read this article on breakpoint chlorination for a more technical run down on how swimming pool shock treatment works.
As the goal is to get rid of chloramines or combined chlorine in the water, you will need to take a reading of this to determine appropriate dosage levels needed. Test the water using a chlorine DPD kit that can tell the different between free and combined chlorine. The testing process is done in two stages. First a free chlorine reading is taken and then a second reading is taken from the same sample to determine total chlorine.
Combined chlorine is simply total chlorine less free chlorine. The total chlorine level and free chlorine level can be equal at times, but total chlorine is never lower. Once you have your combined chlorine reading you will need to add 10 times the amount of free chlorine in the form of a shock treatment. So if the combined chlorine reading is 1ppm you will need to add 10ppm for treatment.
The size of the pool will influence exactly how many pounds of granular swimming pool chlorine, tablets if using swimming pool chlorine tablets, or gallons, if you are using liquid pool shock, you will need to add to (i.e broadcast over) the water. Follow the manufactures instructions and guidance carefully in making this calculation.