Thanks to all your responses, guys.
As I mentioned in my original posting, the water was aerated for nearly three days and the temperature was brought to 78 before introducing to the display tank. I did not bother testing for PH and other things, since I thought this was just one big water change.
All fish are gone and I did not lose a single invert. So I can only come up with the following assumptions:
a) There was no DSB
crash since there was no bad odor.
b) Excessive Flow and/or sand storm killed all fish - I have already corrected the pressure problem.
c) The biggest blunder I think I did was to completely turn off the sump/skimmer/return for the entire night. The powerheads were running but now I doubt their efficiency.
I was wondering if anyone else had gone through a situation like this. Tonight I am thinking of getting a damsel and put it in the tank and see how he copes up.