On the ATO topic. DO NOT set up an ATO directly connected to your RODI unit. I had what I thought was a bullet-proof dual fail safe system with a timer and a float valve. Worked flawlessly for 3 years. Decided to fail simultaneously while I was on vacation for 6 days. Came home to a flooded living room and a brand new freshwater tank full of dead coral and fish. This is why I have a 6-month old reef in my basement now instead of a 6-year old reef in my living room.
Only ever do an ATO with a reservoir that is small enough that you won't crash your reef if the entire reservoir dumps into your system. For example, my 10g reservoir for my 65g tank would certainly make things unhappy and get some water on the floor, but it won't nuke the tank. Your sensor/float valve/timer will fail at some point. I still use an ATO now, but set up so the inevitable oops won't cause permanent issues.
I should really have this warning saved as a quick text; I post it a lot but if I can save one reef by posting this lesson all the time, it's worth it. I lost thousands of dollars in old-growth coral and had a $15,000 homeowners insurance claim (for home damage only) due to this foolishness.
