Still not clear what your goals are - powering your sump pump, notifying you of a power outage, or both?
For the sump pump, many companies make battery backup units, so if you're worried about keeping your basement dry, that's probably the best option.
To sense power to your tank, you need some sort of battery backup for any sensing system. The options I can think of off the top of my head are a separate home alarm system that notifies you of a power outage, or a reef controller with a battery backup, UPS backup power supply. To sense the power status, some UPS units have an interface or alarm light that goes on/off when the unit is on backup power, so you could use that to signal the controller. Otherwise, you could have a relay/SSR connected to an unprotected outlet and have the controller e-mail you when the connection is broken.
If power interruptions are that frequent or that much of an issue, you should consider getting a backup generator; it may well be a better/cheaper option in the long run.