Hi NaturalDisaster0,
Your going to want to make sure the tank water remains oxygenated. This is by far the largest and most pressing issue to worry about during a power outage. Right away I would recommend placing a clean hand in the tank and push the water around for a minute or two. I suggest repeating this at least every 30 minutes to maximize coral and fish survival rates. Your inverts will likely survive the entire ordeal even if no action is taken.
The next thing to be concerned about is keep the temperature above 70 degrees or higher if at all possible. Doing this during a power outage is not going to be easy and is going to require some ingenuity. If you have any hand warmers available, activate them and place them in multiple ziplock bags to avoid leakage, Next, add the bag to the tank and increase the rate at which you push the water around if you can. If this is not an option for you, find a way to heat up a large pot of water with a lid on it. If you have a portable gas stove or a grill, you can heat up the pot of water this way. Do not heat the pot up excessively, but try to bring the temperature to somewhere between 90 and 100 degrees. Following this, put the water in plastic bags or water bottles that will not leak and place them in non-congested parts of the tank. Make sure to keep pushing tank water around and at an increased frequency if possible. Monitor the tank's water temperature and repeat this process as neccessary.
I'll be active for the next couple of hours so please keep me posted. Power outages are never any fun, but quick intervention can save the day.
Drop a like if this helps!