Aquatic Life Farm, LLC

where we only sell tropical fish we raise

Keeping Fish Tips

 How to Survive a Power Outage

by Frank Cowherd

I do not know about you, but when the power goes out, I start to worry about my fish.  Will the power be out long enough to be a factor? When it first goes out, you never know when it will come back on.  Normally it is back on in a few minutes, and I give a sigh of relief.  I am all psyched up to do something to save the fish, so when the lights do come back on, I can relax again.

When people are lost at sea or in the wilderness, there are three concerns.  These are food, water, and shelter.  The priority of one over the other depends on what the weather conditions are.  You will note that oxygen was not mentioned.  Oxygen is 20% of the air we breathe and for the most part any emergency situations in which we find ourselves does not change the amount of oxygen available to us.  This is not the case for fish in an aquarium.

Oxygen and Water

An emergency situation for a fish, your fish in particular, during a power outage never involves the lack of water.  In fact, too much water is usually the cause of the loss of your fish. Two things happen to an aquarium, no matter what size, when the power goes off.  The machines that keep the water moving stop, and the heater no longer produces heat.  These machines mechanically pump water or pump air that then causes the water to circulate in the tank.  Their secondary function is often to pump or suck the water through a filter in order to clean the water.  But filtration is not a critical function in an unexpected power outage.  The critical function of these machines is to bring water to the air-water interface so that the water can become saturated with oxygen and additionally to get that oxygenated air back down to the bottom of the aquarium

What happens to the oxygen content in the aquarium when the power is off?  The water quits moving.  The water at the bottom where the fish are becomes depleted in oxygen because the fish and the decaying matter in the substrate consume it. This depletion of oxygen might happen in just a few hours, but how rapidly the oxygen is lost depends on the number of fish and how clean the tank is.  Only the top couple of inches of water will have sufficient oxygen for the fish to survive when the power is off.  And the fish will tell you that this is happening because they will be at the top sucking air if there is not sufficient oxygen at lower levels..  Those fish that can supplement their oxygen intake by getting a gulp of air at the surface, like corydoras, anabantids, ancistrus, etc., will survive quite well under these conditions.  But those that cannot gulp air can be under real stress. 

If the power comes back on in a few hours, likely you will not loose any of the fish.  But you need to be prepared if the outage lasts longer.

Without agitation for a few hours only the top couple of inches of water in the tank will have any oxygen and it might not be sufficient for the fish.  That is why you find them sucking oxygen from the surface.  So lower the water level in the tank until it only contains one or two inches of water. The movement of the fish in this shallow water helps increase the oxygen content. The fish are providing the agitation of the water whenever they move.

Water - Extended Power Outage

During an extended power outage lowering the water level to a few inches is better than not lowering the water.  But because the substrate in the tank contains decaying material which demands oxygen, you are better off catching the fish and putting them in an empty container, like a five-gallon bucket, an empty aquarium or a child’s wading pool with only enough water to allow the fish to swim upright.  And it’s best to use the water from the tank they were in since that is what they are used to.  If you transfer the water by spraying it from the end of the siphon tube, it will pick up sufficient oxygen.  In this shallow water, the movements of the fish will cause the water to circulate so it can pick up more oxygen from the water surface.  The fish can survive under these shallow-water conditions for more than two days, maybe even a week or more, unless they are really crowded or not in full health to start with.  I have kept 20 quarter-sized angelfish in a gallon of water in a five-gallon bucket for a day without any problems.  Fewer fish could be kept in a similar situation longer.

Check your fish in this emergency container.  If you see a lot of droppings or debris, do a water change with water from the tank they were in or with fresh conditioned water if you have it available.  Again use the siphon and spray the water to get the oxygen to its maximum level. 

The tank the fish used to be in will be fine without the fish and will be ready for the fish in a couple hours after the agitation is back on.  However, if you have a lot of plants in the tank, you might consider lowering the water level so the plants get more oxygen.  Yes, plants need and consume oxygen at night.  Plants only produce oxygen when they get sufficient light.  If you are still worried about your plants, remember that plants can survive for days in a closed plastic bag with only enough water to prevent the plants from drying out.

You can put a few plants in with the fish in the shallow water container to give the fish someplace to hide, but do not put a lot of plants in with the fish because the plants also need oxygen.

And a disclaimer on the use of five gallon buckets or 10 gallon tanks, if you have really big fish like Oscars or other large cichlids, a child’s wadding pool is an option.  These will hold 50 gallons of water and be about 5 to 6 inches deep.  They will keep the large fish alive for many days without air pump or mechanical pump as long as the temperature is right.  But you might have to cover the pool with a screen or net to prevent the fish from jumping out.  And do not place it where it can get direct sun light for more than a couple of hours, as that can cause the temperature to get too high.


Now that you have provided the fish with sufficient oxygen for survival by putting them in shallow water in a bare tank, do not mess it up by feeding them.  They will survive for more than a week without any food.  The right temperature is another thing.

If the weather is mild, the water temperature will not change much and the fish will be fine for many days.  But if it is hot, monitor the temperature.  If it gets above 85 or 90 or whatever temperature they should not be subjected to, add a bag of ice.  Leave the ice in the plastic bag.  A zip-lock bag or plastic bottle with screw top with a few ice cubes should be sufficient.  On the other hand if the weather is really cold and the house is cooling down, heat some water on a camp stove, put it in the screw top plastic bottle or your old hot-water bottle and put it in the tank.  Do not make it too hot.  Use the Goldie Locks rule, not too hot or too cold, but just right.

And another possibility, if the fish are in five-gallon buckets or 10-gallon tanks, they are quite easy to move.  Take them to a friend’s home that has electricity and also the right temperature.  Add an air stone/air pump for insurance and relax until the power comes back on.

A generator will work too, but you have to run it all the time to keep the pump running and the heater working.  You can run the generator for two hours on and then a couple hours off.  How long the tank can be left without the pumps working can be determined by observation of the fish.

You can also get an inverter and a couple of marine deep cycle batteries to keep the pumps and the heater running.  This is a better option than a generator in my opinion, but like the generator, you have to keep them in operational condition year around.  Otherwise, when you actually need them the batteries may be dead or the generator will not start maybe because the gas has deteriorated.  One battery should be good for about 12 hours, but it really depends on how much equipment you are running.  Costs for an inverter and batteries can be less than a generator.

Fortunately, in the six years I have been here (Southern Maryland) there was only one time we were without electricity for more than 2 days. And that time was related to snow.  Hurricane Isabel, which did produce many downed trees and flooded roads, only caused a short power outage for us.  Neighbors with chain saws are a real benefit around here. They allowed the power crews to get in and restore power quickly.


As for food, it should not be a concern.  Healthy fish can go for up to two weeks without being fed.  And feeding can cause problems since uneaten food will decay and use up oxgen in the water.  So it is best not to feed the fish.

With a bit of thought and planning you can get your fish through even an extended power outage. 

September 5, 2009

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