What If Theres A Power Cut?
Short power cuts for up to 30 minutes have almost no effect on an aquarium, but any longer than this and it is worth taking a few steps to ensure your fish come to no harm.
The biggest problem for power cuts of a few hours is not temperature, which will only drop slightly, but the effect on the bacteria in your filter which process fish wastes. Without a continual supply of oxygen through the filter bacteria will begin to die, and may not be able to process all the waste products your fish produce.
If the power cut lasts up to an hour, bacteria in internal filters should recover, but external filters, which are a sealed environment, will suffer. The best course of action is to remove the filter media, if it is very dirty give it a light clean in tank water, and place it in the main aquarium for the duration of the power cut.
After a significant power cut keep feeding levels very light and keep a close eye on water conditions, particularly ammonia and nitrite levels. Give the aquarium a few weeks to recover.
For a more detailed look at what to do have a look at our article on Power cuts in a Tropical Fish Aquarium