I have a Reefkeeper lite that I recently purchased. I would to use that to set up a ATO for my tank as I noticed they sell float switches. My question is: what equipment do I need to purchase for the ATO? Do I need one or two float switches and what additional pumps will I need? Thanks.

Kinda depends on if you want a second float to act as a backup to the first to shutoff the pump. For a larger tank (5gal+) this would be a very good idea. Unfortunately its a bit tougher in picos due to space concerns.

As for a pump, again, kinda depends on tank size, if its fairly smallish, you can use an air-pump to pressurize a jug of water, pushing said water through another submerged airline hose into tank for topoff. This is what I intend on my pico. This is also feasible on larger tanks if evap rate isn't extreme (or the system isn't much over about 40gal or so), otherwise you'd probably need a centrifugal pump to keep up. Unless you've already bought it, I'd get your ATO float-switch from aquahub.com (i-float), or browse ebay. Same thing, less expensive. Either way, you will need to get the switch cable to connect the switch to the RKL, but it looks to be pretty inexpensive, and you get a double ended cable that you cut in half for using on two floats if desired.

Ok. I ordered the float switch kit from Digital Aquatics for the Reef Keeper lite with the hopes of setting up the ATO. Would something like an Aqua Lifter be a recommended pump? Also, would I need to put something in the tubing to prevent any back siphoning? Thanks.

you just need to watch your placement of the pumps and reservoir in relation to the tank/sump.

Yes the Aqualifter pump is a good choice for this type of setup. To ensure no back siphon just make sure that the tube delivering the water to the tank is higher than the full mark of the tank. Like this

Click to view attachment

Here is a crude picture of my setup.

When you set it up you may need to put the pump on #1 or #4. There is an issue with 2 and 3 not shutting off low amp things like aqualifter pumps.

Thanks again. Does anyone know what size tubing I need for the Aqua lifter? Also is there some kind of bracket people use to keep the tube over the edge of the aquarium?

Airline tubing

My tank had a notch that it fit in, you could always cut a notch in the plastic lip if your tank isn't frameless. Else I'd probably just use super glue