Alright, here is my horrible update...
I just got home from a week long trip to visit family in FL and IN (yeah, that should definitely hold me over for another year

). I was feeling pretty good about leaving the tank unattended for a week too. I usually use about 3.5G of RO/DI a week. So, I hooked my ATO up to a 5G bucket full of the stuff. I overfed all the corals and Buck, my lone YCG , in the days prior to leaving also. In a rush to get ready for an early flight, I made the decision to just use a 24" Sundial fixture above the tank. Sure, this is a bit overkill in a 15" wide tank, but a lot of the corals used to be kept under this light, and I was pretty certain none of them would care.
Well f*** me.
I got back today to find the 5 gallon bucket empty, the rear chamber had less than 1" of water in it AND buck was perched (I thought dead) to the bottom of the tank back there. Water was a bit hazy and since my heater was kept in the EMPTY REAR CHAMBER, it has exploded inside itself and the water temp was around 61 Degrees.
Like I said, F*** me.
I estimate that the ATO bucket had been empty for around 24 hours or so. I didn't bother to test the salinity, instead opting to drive like a mad-mad to the local store to pick up some water (from the fridge aisle), heat it up in my sink as quick as possible and get it added back in. The tank has taken almost 2 whole gallons of fresh water. After the temp and water level were back to normal, I did a 10% water change to boot.
Now for the toll. I think I will lose all of my SPS with the exception of my least favorite, a Monti Digitata. Aside from that, some of the LPS, the Duncan colony specifically, is pretty pissed off looking. My two Yumas are shriveled, and the Zoas and Palys seems only moderately pissed off, and making a recovery. Time will tell. Buck is definitely freaked out and I don't want to take him out of the rear-chamber tonight, he has been stressed enough. The good news is that he is eating though. I don't want to lose the poor guy, I have had him for a while now.
I will keep the updated coming. Everyone pray to the coral and fish god for me.