Thought I'd post this for anyone searching later.
So I decided to try it out. So far it's keeping about the level I want. Just below the output of the HOB filter. Don't get that non-stop waterfall noise. It's right at the edge of the trim on the outside though. It wouldn't go any higher without trimming the... uh... trim.
This is how I set it up on my 75g rimmed tank. It took some thinking figuring out how to install it, but this worked for me.
Turn all the tank equipment off to start.
1. Assembly actually wasn't a big deal. It will only go together one way. If one of the plugs into the controller doesn't fit, switch spots with the other one. Other than that, included instructions do their job.
2. Install the box in the tank at the highest possible point. It will fill up, and if the tank is at a similar level to mine, it will fill quite a ways over the overflow sensor. So...
3. Drain the tank to a level just below the bottom sensor. It will also be below the bottom of the skimmer slots. KEEP THE WATER! Ideally the container used to drain the tank should be the same container you're planning on using as the ATO reservoir.
4. Drop the ATO pump into the reservoir of salt water.
5. Plug everything in.
6. The ATO pump will flip on and off as the skimmer box fills and is pumped out into the tank. The skimmer pump will drain the box slower than it fills, so it will repeatedly fill to the overflow sensor and stop untll the water is pumped out of the box and below the low level sensor again.
7. The ATO pump will finally turn off for a while once the tank level and the box level balance out. It will probably take pretty close to all the water you drained earlier.
8. Either dump that last bit of saltwater and refill with fresh, or, as I did, just add the fresh onto whatever salt is left. It was a small enough amount in my case it shouldn't have too big an impact on the DT salinity. But I'll test in the morning and see where it's at.
9. Realize you'll probably have to rearrange the equipment hanging on the tank because you didn't really take your time to plan exactly where everything should go and just threw it on where it would fit.
10. Aaaaand done!
There might be a better way, but this worked out well for me. Hope it helps!
