Lazy: Thanks, thats a good deal but I still top of my tank by hand. When I made my sump I did two things. Made sure that it can handle the drain from the tank when I return pump is off (some people don't!) And that even if my return pump pumps all of the water from my return chamber that the tank won't spill over. That was if the overflow get clogged or stopped, I won't have a flood. You've seen what a flood would ruin
The switch I need is for my frag tank as an emergency shutoff. Since the return pump for my frag tank will not have the same safely measures that my larger pump does. This float will be mounted on my cross brace about 0.5" above the water line. Should the drain on the frag tank slow or get stopped, the water will rise, open the switch, open a relay and turn off the pump.