Forms of chlorine
The main forms of chlorine used include sodium hypochlorite (NaOCl), calcium hypochlorite (Ca(OCl)2), and chlorine gas (Cl2). Sodium hypochlorite is often sold as 12 to 15 % solutions. Calcium hypochlorite usually is sold as a powder or tablets in formulations of 65%. However, it does not dissolve readily (especially in cold water) and undissolved particles can injure fruits and vegetables. To prevent this, first dissolve the powder or granules in a small amount of warm water before adding it to the tank. If using tablets for continuous, slow release of chlorine, ensure that the tablets are placed where water circulates well around them. Chlorine gas comes in pressurized gas cylinders and should be handled cautiously according to label instructions.