Operating a swimming pool, spa, or water feature without an automated controller is analgous to operating your home heating system without a thermostat.  Constantly turning your furnace on and off manually is unthinkable, yet the majority of swimming pool and spa operators control chemistry in exactly this fashion.  Water balance oscilates between "under feed" and "over feed" as operators attempt to maintain chemistry control in conjunction with other work activities. As a consequence unsafe water conditions, chloramine formation, and excessive organic loading are common occurrences.