i have mine set on mode A because that way it protects my resovoir pump from pumping all the water out of my res bucket,if your on mode B nothing is protected and you could run into problems with your pumps running dry and burning up,you can use sensor one as your sump sensor and when it goes down about an inch or so it turns on the pump in your res bucket,sensor 2 i have in my res bucket so when the water gets to low the sensor turns off the res pump so it does not pump out all the water ensureing the res pump does not burn out,i made a vid of how i set mine up,just check out my 75 gallon build thred and you can find the vid
