Spruce, i was going to use a float switch like you said because i was moving house and going to need a static setup, now that has all fallen through, and i need to keep my system in my van which is all automatic.
But now i have a booster pump, but it not automatic, so i bought the contoller in the link, but i thought that the would cut on and off instantly, but they dont, the dry run protection can take a minute to stop the pump, and when the tank in the van is full and the solenoide activates to stop the water it can take 10-15 seconds for the pump to stop, it all work now but i thought it should sense instantly.