Does a power outage cause harm?
What happens in case of a power outage? Does it affect the fish?
damages are not likely in case of short power outages up to approximately one hour. In case of longer outages (considerably over an hour) it is advisable to pull the filter plug if you notice it in time.
Then direct the first water (5 - 10 times the filter volume) running out of the filter (in case of an external filter) into a bucket and pour this water away when the power is back on.
In case of internal filters you should wash the filter media thoroughly in a half filled bucket of aquarium water and pour the washing water away as well.
This washing procedure has the following purpose: The bacteria are not supplied with fresh water when the filter is off, which may cause formation of pollutants (nitrite, among others) which you would then pump into the aquarium if you put the filter back into operation without rinsing it. A nitrite test directly from the water standing in the filter is therefore recommended.
Power outages lasting so long that the aquarium water, due to not being heated, cools down considerably occur, fortunately, extremely rarely. In the worst case, the aquarium must be kept at an appropriate temperature by regularly adding hot water.
Dr. Bodo Schnell