A pond dechlorinator unit is a device that is designed to remove chlorine and other harmful chemicals from tap water before it is added to a pond. Chlorine is commonly added to municipal water supplies to kill bacteria and other pathogens, but it can be harmful to fish and other aquatic organisms in ponds. Dechlorinator units are especially important for newly established ponds or ponds that have been drained and refilled, as the high levels of chlorine in tap water can be lethal to fish and other aquatic life.