What should I do when the red light illuminates on the Clean indicator/reset button?

The red light on the Clean indicator means it is time to clean the transducer/ultrasonic membrane. Clean the membrane using a 50/50 mix of white vinegar and water applied with a cotton swab, then wipe off with a damp cotton swab. After filling the tank with water, press and hold the clean indicator/reset button until the red LED turns off. (Page 7, 9, 12)