I would have them test it on a tank but the osmolator goes through 3 seperate quality checks. The optic sensor is checked, the board is checked and the final assembled unit is checked. A bad osmolator is a very rare occurence. It is usually a particular quirk with the installation, bubbles, EMF interference, etc. Do you use any sort of X-10 or wireless circuitry with the tank? Is the controller near a ballast? What I generally do to trouble shoot is put the sensor in a bowl of water, away from the tank, in the kitchen for example. This way you can determine whether it is the controller or the install and work from there.