Yes, the less bio load helps. One of the reasons I keep smaller fish. My buddy had a 220 stocked with big fish. Within 5 mins of the filters and ph going off, the fish were at the surface. He has a generator, but still..
Just keep an eye on them. May not want to feed or do so lightly while power is off.
With the low fish load, you may be better off waiting on the water change. Like Gerry said, stir the water up, but as often as you can. Invest in a back up power supply, even if it's a simple computer battery back up. There are air pumps that draw very little energy that can get you through times like these. Small generators aren't that much to buy too. Well worth it. Should be part of any tank set up IMO.
The power failure later 36 hours. The fish never seemed stressed in any way. Given that this is probably the second power failure to last more that 6 hours in the past 10 years I don't see much of a need for a generator but a ups may be on option.
I've often thought about getting The Crank a Watt(TM) Emergency Generator for times like this. If you have kids it would give them something to do.
It might be better to remove the water from the tank, aerate it and return it to the tank, if the tap water isn't to be trusted.
This is where an MP10 and a battey backup would come in handy. Also battery operated Air pumps with an airstone would help too. I'd watch ammonia levels too since your filtration is down. But seeing your heater is out too...
Walmart - Battery operated fish bubbler for fishing
The sell them in the fishing section, you could get one and drop it in...or buy a small batter operated bubbler from a pet store and use it to break up the water. I know I read once in Miami during the hurricane that people would actually take a big pitcher and would lift out water out of their tanks and pour it back in from a high height. It oxygenates the water. They mention using hydrogen peroxide BUT only as a last resort and IF your fish are all dying from oxygen issues. They recommend the dumping water from up high and say using a spoon just excites them too much. They even recommend covering up the fish tank as it causes them to move around less thereby using less oxygen. I know down here they deal with hurricanes a lot so power outages are not uncommon and sometimes can last WEEKS.
Interesting. This website says if you have BIG fish to buy a kids wading pool. Apparently, they can survive for days in it and will do better than in a freshwater tank because the water level is lower and they will agitate the water with their swimming. I hadn't thought about that. I wouldn't leave it in the back yard though, you may end up with a raccoon going fishing.