Is it normal to fill up the grey water tank this fast?

Does anyone know how i can get the gauge on my tank working? It constantly shows empty for both the grey and black water tanks. The fresh water sensor works though......i think I could meter the usage better if i could keep an eye on the levels.

Is it common for them to stop working? I don't want to have to rely on water backing up into the tub to tell that the grey tank is full.