We got a UPS 650 to attach to our tank. We did this because we got a notice from the electric company that power would be cut for 6+ hours one day for neighborhood repairs. You have got to keep in mind that you can't necessarily go by the box when it tells you how much time it can run a computer. You must remember that computers eat a lot of wattage. We just hooked up one pump and an air pump with air stone bar so that there was still water movement. We figured that was enough. They don't have to have light. (We have plenty of natural light in the room anyway.) Well, that one pump only takes up like 9 watts and the air pump was not that much either. Our calculation is that the battery in the UPS (since it was new) would last upward of approx. 14 hours with such little wattage being used.
You do need to test whatever equipment you decide to hook up to one though. I don't have the all the terminology right, but bear with me... When we hooked up both circulation pumps that normally run in the tank and cut the power, the UPS kicked on, but the pumps shook for a second or two trying to figure out the new electric cycle. One kicked in fairly quick and was running normal and the other had problems (just shook, but little to no circulation taking place). So, we just have one pump plugged in to the UPS that will run when the power goes out. We didn't trying adding on the protein skimmer or maybe just the actinic lights, but we didn't feel it necessary. To me, the minimum was fine....no need to have everything running during brown outs, just enough for the animals to be comfortable and safe.
All that to say that UPS will run longer than what the box states for a computer depending on how many items you plan on trying to run through the UPS if the power goes out.
That's my unprofessional take on this...
Jody