Occasionally, just about every swimming pool owner has wondered whether common bleach can be substituted for pool chlorine. Such thoughts often arise after you spend good money on yet more pool-specific chlorine. In truth, bleach contains the same base chemical as pool chlorine. That chemical is, of course, chlorine. The major difference between the two types has more to do with strength and formulation than anything else. Also, bleach is a bit less expensive than pool chlorine.
The most common form of bleach sold for household use contains sodium hypochlorite chlorine as its main disinfecting chemical. Sodium hypochlorite chlorine is also the common liquid form of chlorine, which makes it perfect for bleach. There is approximately 5.25-percent chlorine content in typical standard household bleaches. Outside of the chlorine, bleach is mostly composed of water and a very small amount of salt, which is necessary to keep chlorine gas in a liquid state.
Common pool chlorine is usually made up of calcium hypochlorite chlorine at about 65-percent strength. The calcium hypochlorite form of chlorine is a solid rather than a liquid or a gas, which is chlorine's natural state. In addition to the chlorine itself, calcium and other inert ingredients make up the remainder of the chemical. Calcium hypochlorite is often used in pools precisely because it's a solid and can be easily introduced into pool water.
Using bleach in a pool has its advantages, including convenience. You can simply pour bleach straight from the bottle into a pool's skimmer. Bleach is also inexpensive in comparison to standard pool chlorine. As of May 2011, bleach sells for about $2 per gallon-size bottle. Pool chlorine is often more expensive by comparison. If there's a disadvantage to bleach, it's that it's comparatively weak when matched against pool chlorine. In other words, you will probably need more on hand.
Calcium hypochlorite chlorine is made specifically for water disinfection purposes, especially in swimming pools. Being formulated specifically for pool use is pool chlorine's primary advantage. It can be introduced into a pool as either a powder or in tablet form. Those tablets are often slow-release, introducing steady but low amounts of chlorine without the need for regular monitoring. However, calcium hypchlorite can be expensive. As of May 2011, a 25-pound bucket typically sells for $90 or more.
In the end, determining the chlorine pool disinfectant type you'll use in your pool depends on what's most important to you. If controlling cost is important, bleach can be a bit cheaper to use. One gallon per week in a pool would run you $2, while pool chlorine would run $3.60 per pound ($90 / 25 lbs. = $3.60). However, if you're more comfortable with chlorine made specifically for pools, then opt for standard calcium hypochlorite pool chlorine.