The most widely-used chemical that pool owners use to kill bacteria, living organisms, ammonia, and any other contaminates (such as dirt, debris, and algae spores) that are in pool water. The two most common forms of chlorine used by pool owners are granular chlorine (whose scientific name is "Dichlor") and chlorine tablets (whose scientific name is "Trichlor"). Chlorine tablets come in two sizes: 1" tablets and 3" tablets.