A chlorine treatment apparatus includes a housing with a cavity containing a chlorine generator for chlorinating a liquid such as water and at least three openings to the cavity. The chlorine generator may be an electrolytic cell. Some embodiments may include one or more plugs for closing the openings. The plugs may be keyed to operate with only certain of the openings. Yet other embodiments may include sensors for monitoring various aspects of the liquid such as temperature, salinity, flow rate, and chlorine concentration.