Yes, upon completing the water change it is adding water and filling past the sensor. Im trying to figure out why it would turn on right after the water change when the sensor is wet. You would think seeing the sensor is wet, it wouldnt allow the pump to turn on.I have a minimum off time of 30 minutes set on mine. With that it should not turn on for 30 minutes after it is on. Is it adding too much at the minimum of time with it full if so you might try a 5 second minumum.