Abstract: A control system for automatically maintaining a predetermined water level in a swimming pool includes a multi-contact water level sensor unit mounted on an exposed sidewall of the pool. The sensor unit is vertically adjustable within a stationary mounting bracket to enable user adjustment of a selected normal water level. A single sensing contact on the sensor unit senses the presence or absence of water at the selected normal level. A monitoring circuit associated with the sensor unit interrupts operation of the control system in the event that the sensor unit is disconnected. Additional water level sensing contacts open a dump valve to preclude overflow of the pool in the event of a high water condition, and interrupt operation of recirculation pump apparatus associated with the pool in the event of a low water level.

Abstract: Concentrated solutions of sodium sulfite and related compounds can be inhibited against sodium sulfate precipitation by substituting potassium for a portion of the sodium contained in such compounds. A typical concentrate would contain a water-soluble sulfite mixture comprising sodium and potassium sulfite with the sodium to potassium ratio ranging between 1:1 to 15:1.