[reefgeezer]

I use food grade liquid level switches, a small 12VDC powered solenoid, and a Brute for my DIY gravity fed ATO. It's bulletproof and has been operating for years without fail. It also keeps the level within about 1/2". All I have to do is fill the Brute every 3-4 weeks.

3 switches are wired in series to control power to a normally closed solenoid: 1) a normal level switch closes when the level drops below the desired sump level and opens when the level returns to normal; 2) a high level cut off opens when the level rises too high; and 3) a low level switch opens when the level falls too low to protect the solenoid from over heating. Finally, a Kent mechanical float valve is installed as a final fail-safe. It will cut-off flow if the sump get just slightly higher than the high level switch level.

The switches are about $12 each, the solenoid is about $20, any little 12 volt power supply will run the thing. You probably have one laying around the house or can buy one a Radio Shack for a few bucks. The load is very small, but make sure all the components are rated accordingly.