If you have a generator already, then don't worry. You are 90% there. You can plug you pump (filter) into that and run it. If you don't want to run it the whole time, then maybe 2hours off, 1 hour on. The biggest problem when the power goes out isn't the oxygen. It is the fish poo, and other junk building up in the water. Plus running your filter will take that out, plus the benifit of circulating your water. If it was just a matter of putting oxygen in your tank, you could just take a picture or a big cup and take water from the tank and pour it back in from about a foot above your tank, This would put air bubbles in the water for a little while. Next to the fish poo building up in the tank, other big concerns should be temp. Tank getting warm or cold. If it starts getting warm, you will need to go get bags of ice. and float it in your tank, make sure not to let the bag leak the water in your tank. Chances are that won't be RO/DI water.