With the new set up, I've tried to avoid holding anything back and went "all in" so to speak. So I got busy one night, wiring up this ultra safe system by Aquahub. The way it works: You have two float switches wired in series, which are powered with a 12v DC power supply. When the switches are down, a relay opens the flow to a 110v power cord to supply power a pump that can push top off water from a reservoir into the sump. As the water level rises, the float rises and cuts power to the relay, which stops power to the 110v cord shutting off the feed pump. If one float fails, the second one is a back up to make sure power is cut to the feed pump.

Installing the floats was easy. My sump had two float switch brackets glued in and pre-drilled. Threading the cord up through the hole, I placed the switch in position, and screwed the nut in place to keep it secure. Then I screwed the plastic round tube to the top, filled it up with silicone and pressed 1/2 tubing down over the plastic piece. This creates a dry zone even if the water level rises in the sump. For safety, I went ahead and filled the tops with silicone as well.

Using the instructions on the website, I followed the images and directions to wire the switches first, and test it. Then the 8' extension cord was wired in and the system was tested again. 

The tools were simple - most people have these on hand.

The one thing I did differently was to use these little low voltage connectors. 

After I knew everything was working, I modded the enclosure box to permit the cord to come out each end.

This is what you end up with, although cord lengths may vary based on need. The black transformer powers the relay, and the plug on the left feeds power to the outlets on the right. The black 'project' box keeps the relay assembly clean and dry.

I'm using an Aqualifter to move water from the reservoir to the sump. It needs a mere 3w, but with this kit you could use a larger pump without concern. Don't use a pump rated greater than the extension cord can handle; usually for top off we don't need a fast pump but rather just enough to get the job done quietly.

Using zip ties, I affixed the box to the center beam of my stand.

I had some cable management tubing to keep the wires tidy. Note how I keep the outlet tied up where it can stay dry.

The same tubing gathered up the fine wires from the two floats.

The two cords run to the DJ switches at the end of the tank. I can flip off either switch to turn off the ATO system whenever needed, like during a water change.

When the water is being topped off, this tall tube keeps the water from splashing and prevents siphoning out too much water if the reservoir is full.

It's working perfectly, and I'm very happy about that. Top off is pretty important, and not having to lug water to the fishroom any longer is wonderful. Having a safe top off system installed to replace evaporation is key to making this hobby more enjoyable.

The vertical tube (pictured above) is on an acrylic riser plate I made.