Thanks for the idea. I have been looking at lifereef Float Valve Switch.
Here are the specs.
This float switch can be used as a refill switch or a pump shut-off switch. Use to automatically add water to your system from a reservoir container or use to control a reverse osmosis (R/O) unit. For R/O setup order the float switch solenoid unit. The float assembly slips into sump accessory shelf in Lifereef filters or for other filters we make a Bracket that attaches to your sump whether it be an acrylic sump or and aquarium type sump. This switch can also be attached to an aquarium rim if you don't have a sump and thus control the aquarium water level.
Simple to set up and operate, the float switch goes in the sump or aquarium and connects to a control box. Your main pump, refill pump, or R/O solenoid plug into the control box. The control box does all the switching so there is very little load on the float switch allowing it to last longer. The control box has a 10 amp rating. Switching is controlled by a solid state Triac not a relay that may stick or make noise. This is THE ONLY switch that does NOT put 120 volts in your water!!! The float switch material is completely salt water safe and is baffled so that waves do not affect the float.
This switch is unique from any other in that the float and control box are separate units and if either one fails it can be replaced without having to purchase a whole new unit.