I would not rush out to buy a generator at this point. Cat's already out of the bag, so to speak. I always have a few battery air pumps ready to go justincase. In the mean time, if you can help to keep the water oxygenated that will go a long way to preventing losses. You can do that by just using a pitcher to scoop up and pour water back in to the tank. More splashing is better in this case.
For future planning, lots of people use a computer ups to buy some time - it would only need to run a power head or two. Looking at the size of your tank, however, a portable generator may be a good choice. If the electricity fails frequently in your area, you may even look at an automatic whole house generator, but that will be somewhere north of $3000 (plus install).
My tanks have been ok with outages up to about 20 hours, so don't panic. Yet.