Abstract: A monitoring system for a water scalping sand classifying tank, comprising timers for measuring the cumulative total discharge times for at least two key classification stations of the tank over an extended period of time which may include many reblend cycles for the tank. Tolerance limits are established by use of at least two timers for each key station. Any extended variation in the desired ratio of total discharges for the key stations, indicating an input change requiring correction, is signalled by an indicator system coupled to the timers.