Bingo! That solenoid is what I'm looking for on that end. Hook that up to my RODI to fill my staging barrel. Then my ATO can be supplied by the barrel to the sump when the float valve opens/closes dependent on water level.

Karin, am I seeing your float valve right? It's in your fuge? Is your return water in the same chamber as your fuge macro?

Kristy, I should have said seasonal water evap. During the winter I use heaters to keep my water up to 78-79. Water volume prevents a rapid temp swing so when the weather (or house) temperature fluctuates out of norm it's gradually felt in the tank with no worries. I have one fan in the canopy that since I've returned the tank to its current location I haven't been using because I've been far too lazy to hook it up to the timer. I used to run it an hour after and before lights on and off. My entire canopy is enclosed and the top is vented so I've very little exposed surface water in the display to contribute to water evap. I don't run a fan in the sump because my water doesn't get hot enough for that, although I used to in my 100 gallon setup.

I would like to get something that will control (instead of a timer) my heaters and fan respective to the temperature of the water. So far those units are an arm and a leg. Of course I think it's more interesting to want something I can't afford rather than to get be able to afford it outright. Makes installing it a grand event. Weird huh?