What Kind of Chemical Is Pool Chlorine?

Chlorine

• First discovered in 1774, chlorine belongs to the halogen class of elements. It's closely related to bromine, flourine, iodine and other halogen compounds and ions. Halogens are also the only group of chemicals that can be made into liquids, solids and gases. That fact can make chlorine particularly useful in a variety of disinfection roles. Chlorine was first used specifically for disinfection of water in 1850, when London, England, used it to combat cholera in city water supplies.
  
  

Calcium Hypochlorite

• There are several different varieties of chlorine that can be used to disinfect swimming pool water. The most common type of chlorine for that purpose is calcium hypochlorite. It's also known as the solid form of chlorine because it most often comes in a granulated powder. It can also be purchased in tablet or stick form in both slow- and fast-release formulations. The actual percentage of chlorine varies, but 65 percent is usually its average strength.
  
  

Sodium Hypochlorite

• Pool chlorine can also be obtained in liquid form as sodium hypochlorite. That form of chlorine is also what's found in liquid bleach. The only difference between the pool chlorine and the bleach forms is the percentage of chlorine in each one. Pool chlorine usually contains 12 percent to 13 percent sodium hypochlorite. Bleach, on the other hand, is typically about 5.25 percent sodium chlorite. However, bleach can be used to disinfect pools if enough is used in the proper manner.
  
  

Gas Chlorine

• Gas chlorine for pools is the purest form of chlorine there is. In fact, gas chlorine is 100 percent chlorine. It's extremely rare for private pools to use gas chlorine, though, because it takes work to use it properly. And though gas chlorine itself is the cheapest of the three forms of chlorine, the equipment to use it isn't. Additionally, a mistaken belief that gas chlorine is too dangerous to handle safely has also limited its appeal among home pool owners.
  
  

Safety Considerations

• No matter its form, pool chlorine is considered a hazardous material. It's halogenated, for one, which makes it a highly reactive, potentially dangerous substance if it's not used properly. Always treat any type of pool chlorine with a great deal of respect, using it only according to direction. Also, never mix two different types of pool chlorine together. Chlorine's reactivity can lead it to combine explosively or to create a harmful gas that can be breathed in.