How to Manually Generate Heat in Your Aquarium If the Power Goes Out

Cichlid tank decorated with live and fake plants

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Before the invention of electricity, people were keeping fish in aquariums. Even tropical fish could be kept with a few "modern advances" to keep the fish warm. Back in the day, external heat sources, such as small gas burners, were placed under the aquarium to keep the fish toasty. Aquariums were specially designed with a bottom that would retain heat, unlike the glass or acrylic tanks we are familiar with today. If you lose power, be ready to ensure your fishes' survival with the following steps.

As soon as the power goes out, make sure your fail-safe devices have activated. This includes backflowing airline tubing and sump shut offs so that water doesn't drain out of the aquarium. If you have a heated tank, retaining the heat in the water is critical. During winter, you should insulate your tank and all filtration by wrapping them in blankets, towels or cardboard. Don't forget to cover the top of your tank, but make sure you do not cut off the oxygen supply.

Resist the urge to frequently check your fish. Every time you take off the coverings, you will let heat escape. Position your thermometer in your tank where you can take a peek at your fish and their current environment without unwrapping them. You will need an "old fashioned" glass thermometer to keep tabs on your temperature, rather than an electronic one! Battery-operated digital thermometers will still work, though.

If you are unable to insulate your tank, you may need to add hot water bottles to keep your tank temperature elevated. Keep in mind that this method is trickier and can lead to wider temperature swings. Use containers that are fish safe and always condition your water just in case some leaks out. Do not re-use containers that have previously contained household cleaning products. If you have a gas water heater in your home, you should still have hot water and can change out the water bottles as needed to keep the aquarium water warm. An electric water heater will no longer work in a power failure, but the water in the heater tank may stay warm for several hours.

If you have a gas stove you can also heat water in a pan to place into the bottles to warm the aquarium. Do not use boiling water in your hot water bottles. If you are attempting to maintain your aquarium water around 80 degrees Fahrenheit (27 degrees Celsius), you should use water around 100 to 120 degrees Fahrenheit (38 to 49 degrees Celsius). You will need to replace your water bottles frequently, but your tank temperature will not fluctuate as widely. Wide temperature swings can be worse for fish than a slow, gradual cooling.


In order to provide your fish with critical oxygen, invest in a few bait bucket aerators. These run off batteries, rather than plugging in, and are a good investment for any fish keeper. As with all aeration equipment, make sure the battery packs are kept above the water line of the aquarium. This way, if the batteries give out, the water in your tank will not accidentally be siphoned out.

Place one aerator in the middle of your tank or two at opposite ends of the aquarium. Aerators will drop your water temperature closer to ambient air temperature, so placing them higher in the home will keep the air they are adding warmer. Try to insulate the airline tubing if possible.


Do not cover the battery units. This can cause them to overheat and stop working.

Water Quality

During periods of no power, you will need to focus on tank temperature and water quality. Do not expect any of your biological filtration to be working properly. Test your water quality regularly and make sure you are ready to do extra water changes. This may require storing extra water in order to have enough warm to do water changes.

If you are planning on doing a water change for a heated tank, you will need to bring your water temperature to that of the aquarium water. Heat a small portion of your new water and slowly add it to room temperature water to bring it to the correct temperature. Never add boiling water directly to your aquarium!


In order to decrease your fish's ammonia output while the biological filter isn't running, you will need to reduce their diet. Thankfully, usually at cooler temperatures, your fishes' metabolism will slow and they will not be as hungry. Depending on how long you expect to be without electricity, you may need to feed your fish and other aquatic animals a very small amount once daily in order for them to survive.

If you feed your fish a frozen diet, it will not stay frozen long without electricity. You can pack it with ice in an ice chest to keep it longer if the freezer power is out. If your frozen diet becomes unfrozen, you need to feed it right away or toss it. Do not attempt to re-freeze as this could damage the product and make the food unsafe. If you normally only use a frozen diet, you may need to get some flake or pelleted food to use while the power is out and frozen food is unavailable.

Critical Steps to Keeping Your Aquarium Toasty

  1. Check fail-safe systems as soon as possible.
  2. Insulate your tank, top and filtration included.
  3. Add battery operated bait bucket aerators.
  4. Monitor temperature at least three to four times daily.
  5. Add warm water bottles as needed to keep the water temperature at the appropriate level.
  6. Test water chemistry daily. This includes your nitrogen cycle, pH, and kH at a bare minimum.
  7. Resist constantly checking on your fish. Every time you take a peek, you are letting heat out.

Susceptible Species

There are many species of fish that do not fare well with temperature discrepancies. Certain marine tropical fish are very picky about their water temperatures and are most susceptible to problems when you are unable to maintain a consistent water temperature.

Species with low tolerances for poor water quality will also be at severe risk. Since your biological filtration will not be able to function, you can expect an increase in the ammonia level of your tank. As with temperature, marine fish and coral species are the least tolerant of elevated ammonia levels and will need to be accommodated in order to survive.

Corals will also require UV light in order to photosynthesize. If you are unable to use your tank lights for a few days, you can expect your corals to suffer slightly. Some coral keepers will use mirrors to reflect sunlight to their tanks to give them light exposure. Beware, this method will increase your algae growth as well!

Best Species to Survive

Species that will tolerate a long-term power outage are those that can tolerate a wide variety of water temperatures, those that do not require a heater at all, and those that are not overly sensitive to periods of slightly poor water quality. Some tropical fish will die if the water temperature drops below 65 degrees Fahrenheit, but many carps, such as goldfish and koi, and minnows such as the White Cloud Mountain minnow are tolerant of cool water temperatures.

Goldfish (Carassius auratus)

Many carp species, such as goldfish, are hardy survivors. They can tolerate a very wide range of temperatures and dips of poor water quality. Standard comet goldfish tend to be sturdier than fancy varieties.

Zebrafish (Danio rerio)

These small, striped fish can tolerate temperatures between 64 to 75 degrees Fahrenheit (18 to 24 degrees Celsius), or fairly stable indoor room temperatures. They come in short or long-fin varieties and even neon colors.

Advanced Planning

What should you keep in your tool kit to plan ahead of a power outage? If you know a loss of power is coming, you can get a jump start on preserving your aquarium temperature. Here's what you should have on hand:

  • Insulation materials (blankets, towels, etc.)
  • Bait bucket aerators
  • Standard glass aquarium thermometer
  • Extra water for water changes and water conditioner
  • Ability to heat water (stove, fireplace, etc.)
  • Clean plastic water bottles to fill with warm water and put into the aquarium

Keeping Systems Cool

Those of you running chillers to keep your aquarium temperatures down will be in a similar situation as those without enough heat if the power goes out. In the summer, in hot areas that rely on air conditioning, over-heating aquariums can also occur in power outages. Here are a few tips for the opposite end of the temperature spectrum:

  • Allow air to circulate around your tank and all your equipment. Use fans if necessary.
  • Minimize or eliminate exposure to direct sunlight.
  • Take the lid off your aquarium and replace with netting.
  • Add additional aeration as explained above. Do not insulate the airline and keep the units above the water line, but in a cool location.
  • Use ice in bags or bottles placed in the aquarium to keep the water cool.
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  1. Dealing With Aquariums And Ponds During Power Outages. North Carolina State Veterinary Medicine.