I recently had a over 48 hour power outage (Toronto) and thought it might be useful to share my experience. I run a 110g display - lots of tangs, SPS and NPS with a high bioload. I have a 8 gallon nano (clown with 2 gobies) and a 20 gallon qt (small clown trigger and baby 6 line wrasse). When I woke up Sunday early am there was no power (I found out later it went out Sat evening). The outside temperature was -1. The tank temperature had dropped to 72F and was dropping. All the fish were struggling and breathing hard. I tried different means to manually increase movement and agitation but nothing was working. I realized I had to buy a generator or face a total tank crash. After several trips to different stores I managed to buy the last generator on the floor at Costco (an ordeal in itself). When I returned I saw there were 2 casualties (flame angel, kole tang - there were actually 3 - i just didn't see the purple dottyback). All the fish were now lying on their side and struggling. This is the product of about 8 hours w/o movement/aeration. I got the generator set up and ran the return pump/powerhead/skimmer (for aeration) and heater. All the fish began to recover. I was running the following: display - return pump/skimmer/powerhead (wp60)/2x300W heater and a 150W heater, nano - 50W heater, skimmer (for flow and aeration) and air stone via air pump, qt - 150W heater and airstone via air pump. By evening the outside temperature had dropped to -12. My room temperature was now at 55F. I was struggling to keep the tank temperature at 70F. The qt tank had dropped to 62F. I did some math and figured i could run a space heater (1700W) and kept a butane stove running to increase the room temperature. The display tank temperature stayed at 70 and my room temperature stayed around 57-58. Things stayed that way until Monday night late and the power came back on. All-in-all I didn't have any more losses in corals or fish. There three fish that i did lose i had for over a year so it kinda sucks to lose them. This is what I learned from the ordeal. 1) Invest in a generator now. If you have a tank that represents a substantial investment over time a $400 generator is not a significant investment. Power outages are unforeseen incidents and you would hate to lose your entire stock during an outage. 2) Aeration/Movement is much more important than temperature during an outage. I was never able to get the tank temperature above 70 in the display tank but yet all my fish started to recover and was actually quite active after a while. My clown trigger made it through 62F for the most part. I am 100% sure my losses were due to lack of oxygen. 3) If you live in a northern climate you will need a generator that can power a space heater. When the outside temperature and room temp started to drop - even with 2 300W heaters and a 150W heater - i couldn't keep the tank temperature from dropping. It wasn't until i ran the space heater and stabilized the room temp at 58 that i was able to keep the tank temp at 70. Heaters will only do so much when there is a big difference in tank/room temperature. My generator was rated for 4500W - i think that's the right size. 4) Corals don't seem that affected by lack of water movement/aeration/temperature. I'm sure there is a break point here but all through this ordeal my corals looked great. I'll update everyone if there is some RTN/STN event in the next few days. 5) At a minimum buy some battery operated air pumps. These will increase oxygen exchange in the water. Sure wish i had one. It might have saved a few losses. Most of these take D cells and depending on the size of tank, it may just be enough. Hope that helps!