After looking into this a little deeper I am now leaning towards an optical float switch and a solenoid valve. Probably build something along the lines of the optical version on Autotopoff.com. Might even get lazy and just buy one.

Anyone know a good source for optical float switches? I don't think the solenoid valve should be too hard to find.

+1

If you need the mechanical valve so your auto-top off reservoir can draw water directly from your house, you should set it up to fill a bucket/container next to your sump. Then have a Tunze system with the pump in the bucket.

The risk will be that if it fails, you'll end up with a flood on your floor, but that's a risk regardless. At least this way if the mechanical valve fails you'll still have your tank in pristine condition to console you while you're replacing your flooring.

The other option is just having an auto top off reservoir you fill manually next to your tank with the Tunze auto-top off. Less ideal because it requires work, but I fill mine maybe once every 4 days, and if I have to go out of town for longer than that, I can set up a larger rubbermaid in front of the tank and put the Tunze pump in it (just remember to also move to output end of the hose on the main tank if you do that as well!)

+1, I too use the Tunze. It has never failed me and is probably to most reliable as it uses a IR sensor instead of a float switch for your water level monitoring. Also comes with a float switch to sense too much water if the unit itself ever goes crazy on you.

It will cost you $200 or more, but well worth it.

The biggest downside with the tunze is the adhesive tabs that secure the controller to a vertical surface. They are almost guaranteed to peel off at some point, and when they do, they will fall on whatever is below them.

Mine fell in to the auto-top off bucket and promptly died. Thank goodness it was pure fresh water, so all I did was unscrew the casing and point a hair dryer at the circuit board until I was sure it was dry.

6 months later, the thing works like a bloody charm. I'll never run a tank without one.

I'd screw it to the wall next time though...

Hmmmm, mine never came with adhesive, I have actual brackets, tracking and all the accessories to mount it nicely. I guess they changed it from when I bought mine a few years back.