On most occasions when urgent attention is required the aquarist can provide it. There is one occasion however when he/she often cannot, or at least not directly.
This occasion is the loss of the electricity supply. The chance of this happening is quite low nowadays because of modern technology. It could happen though. Perhaps supply cables or other equipment have been struck by lightning, or equipment has been flooded. The equipment itself could unexpectedly fail.
The electricians will work as quickly as possible to restore the supply, and it is usually back on in an hour or two. It is possible for the loss to continue for many hours, or even days. In my area torrential rainfall caused the catastrophic failure of an essential piece of equipment. The electricity company hadn’t a spare locally and sent away for one, which took four days to arrive. However, they provided a generator for the main part of the waiting period. I remember going to look at it, the generator and diesel were very large.
Whether the aquarist maintains a fish only or reef aquarium there are dangers. It is obvious that if the electricity supply fails all the equipment servicing the aquarium will stop.
If the failure is in the aquarium dark period then there won’t be any sudden light loss, but there will be if the lights were switched on. The fish may flash about a little before hiding, but they are not likely to be damaged as there is usually enough daylight in the aquarium to assist with direction.
What aquarists are mainly concerned about is heat loss. This is quite correct in that there will be a temperature reduction, the amount dependant on the length of the electricity failure. Is it the main concern though?
Retaining heat is fairly straightforward. Use blankets to wrap the aquarium all over which will act as insulation. Seawater cools down relevant to the surrounding air temperature, so if the air is warm the loss will be very slow. If it is cold the loss will be more rapid.
Seawater cools down much more slowly than many think, and usually the electricity is back on before there is any serious problem. When the heaters are back on the two or three degrees lost are soon regained.
Large aquariums cool more slowly than small ones, so the aquarist with a nano for example needs to keep a more regular check.
If the seawater is cooling down and the aquarist wants to counteract it then, using clean glass bottles, heat tap water and place it in the aquarium in the bottles. (Be sure the glass doesn’t crack from the heat.) Repeat this as often as necessary. The tap water can’t be heated using electricity of course, but there is often a gas camping stove etc that could be used. The aquarist will need to counteract the aquarium water becoming stratified, that is, warm at the top and cooler lower down, by gently stirring it on occasion with a wooden paddle of suitable dimensions, or something similar.
The question whether heat loss presents the main problem was mentioned. Heat loss is not the main concern. As said, seawater is slow to cool and the heat loss can be counteracted quite easily.
The main problem is oxygen. This applies to any system type, but particularly to heavily stocked fish only ones.
The fish and other livestock, including the bacteria inhabiting the bio-filter, continue to have a need for oxygen. There is a finite amount available in the seawater, but under normal conditions it is being continually replenished. The oxygen is replenished at air/water interfaces including the aquarium water surface, the protein skimmer, the weir, the sump water surface etc.
For oxygen replenishment, or gas exchange, to take place there needs to be water movement. Without the water movement nothing happens. So the oxygen reserves in the seawater reduce until it becomes critical.
As mentioned the danger is most severe in a heavily stocked fish only system. Reef systems, though at risk, are usually stocked much more lightly as this assists with water quality.
The problem can be combated simply. Have a reserve power supply available. This could be a small petrol driven generator, a battery driven circulator (depending on the size and stocking of the aquarium) or a UPS (Uninterruptible Power Supply).
A reserve power supply does not need to run the whole aquarium system. It should have the capacity to run the heater and circulation pumps (the return pump in the sump if there is a sump, and the display aquarium circulation pumps). If a petrol powered generator is being used and it has the capacity to run all the equipment, then why not? If a battery powered circulator is in use, then that is the only piece of equipment that will run. If a UPS is in use, then, as said, it should be used for heaters and circulators only to lengthen the period of batter power that is available.
The possibility of a power failure is the initial basis for consideration of a back-up system. The second consideration is the likelihood of a lengthy outage. The third consideration is the bio-load, particularly fish, kept in the system.
Underlining all the considerations mentioned is the welfare of the livestock, never mind the sadness of the aquarist at any losses. Some of the back-up methods are not cheap, but if money is a consideration – as it usually is – then consider the cost of the aquarium system set-up plus the cost of live rock and livestock. This sum will usually outweigh most back up systems.