Water level control
Hi,
A simple way is using a linear pot with its shaft tied to a one turn (270°) screw ( a helix ), made of a piece of rigid plastic strip going from the bottom to top of the tank. A float, with a weigth attached, and a parallel guide, will turn the pot from top to top following the water level.
The voltage obtained can be represented in a bar-graph display, and a pair of comparators will set the start and stop points for the pump motor.
A security independent float-microswitch, will assure an electrical stop in case of electronic failure.
I hope this will help you. Regards.