Abstract: An automated control system for maintaining a supply of dissolved oxygen (DO) within a given range in each of a given plurality of pools for treating sewerage, farming fish, or the like, and energizing an alarm system (148 FIG. 1) which, when energized, will warn designated persons of the failure to maintain the amout of D.O. within the given range in a particular pool and with each pool comprising a first sensor for sensing the amount of D.O. in each pool, a settable indicator (146) for detecting, respectively, when the amount of D.O. drops below a first threshold and when the amount of D.O. drops below a second threshold, with both the first and second thresholds being selectively determinable by setting the indicator. Also provided is a communication link for transmitting the amount of D.O. to the indicators, a second sensor responsive to the amount of D.O. dropping below the first threshold (146) to energize the pool aerator (258 FIG. 3) to increase the amount of D.O.