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Did circulation on the tank stop as well??? I am thinking the fish were sluggish because they were slowly running out of oxygen if circulation stopped in the power outage. Once things got fired back up oxygen levels rose and the fish responded. I had a similar event without the temp drop...A boatload of CO2 dumped into the system thus robbing the tank of oxygen during the night. Once I woke up and found my tank looking terrible I did a water change as the first response. The fish responded quickly and eventually i found out about the CO2 issue. But in the end the fish were so stressed from the whole event that 50% of them perished over the next few weeks from ICK. The corals were fine, but no temp drop. I think you will see over hte next month or so which corals were more stressed and those that could handle the temp variation. Maybe you will get really lucky and everyone will be just fine as it sounds like you caught it fairly quickly.
Good Luck and keep us posted.