Electricity Due To Go Off For 7 Hours Next Week. Will This Be A Problem?

Will you be at home while this happens?

I also had this happen a couple of years ago and came through with no problems

Internals aren't usually too much problem as the oxygen in the water can easily diffuse into the media from the water.
Externals are different as it takes a long time for oxygen to diffuse down the tubes. With these, open the filter and put the media in the tank.

To keep a tank warm (if the weather takes a cold turn) get the room warm before the electricity goes off. If necessary, wrap the tank in blankets, old quilts or whatever you have to hand.

Don't feed the fish the day before to reduce the load on the filter bacteria.

Keep an eye on your ammonia and nitrite for a few days to be safe.

I forgot to mention to feed the fish less food than usual for a couple of days after as well. That way if you do lose some bacteria there will be less stress on the ones left till they've multiplied. If you do get a mini spike in ammonia and/or nitrite, it should be over quickly.

Look on the plus side - at least your fish won't be making very much ammonia if they aren't fed for a few days 

Look on the plus side - at least your fish won't be making very much ammonia if they aren't fed for a few days 

Very true Sue!!

My fish went mad this morning when I put the filter media into the tank, they are asleep when I got in last night so it was there first chance to beg for food done I left them! Having to ignore them though, poor things!

I've just discovered that not only do I have no power but I also have no running water at all!! Very unimpressed. I was expecting to not have hot water but not sure why I have none at all. 

Fingers crossed the tank settles again after this