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

Cichlid tank decorated with live and fake plants

mtreasure / Getty Images

Before the invention of electricity, people still kept fish. Even tropical fish could be kept with a few "modern advances." Back in the day, external heat sources, such as small gas burners, were placed under the aquarium in order 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 sure to be ready with the following steps to ensure your fishes' survival.

As soon as the power goes out, make sure your fail-safes have activated. This includes backflowing airline tubing and sump shut offs. 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" thermometer to keep tabs on your temperature, rather than an electronic one!

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. Do not use boiling water in your hot water bottles. If you are attempting to maintain around 80F (27C), you should use water around 100-120F (38-49C). You will need to replace your water bottles more 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 systems run off batteries, rather than plug ins, and are a sound investment for any fish keeper. As with all aeration systems, make sure the battery packs are kept above the water line of the aquarium. This way, if the batteries give out, your tank will not accidentally be back siphoned. 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 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 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. Boil a small portion of your new tank water and slowly add it to room temperature water to bring the temperature into the correct range. Never add boiling water directly to your tank!


In order to decrease your fishes' ammonia output, 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 in order for them to survive.

If you feed your fish a frozen diet or supplement, it will not stay frozen long without electricity. If you only feed a frozen diet, you may need to supplement with a pelleted diet for a short period of time. If your frozen diet becomes unfrozen, you need to feed it or toss it. Do not attempt to re-freeze as this could damage the product and make the food unsafe.

Critical Steps to Keeping Your Aquarium Toasty

  1. Check fail-safes ASAP!
  2. Insulate your tank, top and filtration included.
  3. Add bait bucket aerators.
  4. Monitor temperature at least three to four times daily.
  5. Test water chemistry daily. This includes your nitrogen cycle, pH and kH at a bare minimum.
  6. 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 tropicals 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 a small increase in the ammonia level of your tank. As with temperature, marine fish and coral species are the least tolerant of these levels and will need to be accommodated in order to survive.

Corals will also require UV light in order to survive. 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 some exposure. Beware this method will increase your algae growth as well!

Best Species to Survive

Those species that will tolerate a long-term power outage are those that can tolerate a wide variety of temperatures or do not require a heater at all, and are not overly sensitive to periods of slightly poor water quality.

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 64-75F (18-24C), 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 temperature. Here's what you should have on hand:

  • Insulation materials (blankets, towels, etc.)
  • Bait bucket aerators
  • Standard thermometer
  • Extra water for water changes + conditioner
  • Ability to heat water (stove, fireplace, etc.)

Keeping Warm Systems Cool

Those of you running chillers to keep your aquarium temperatures down will be in a similar situation as those without enough heat. 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.
  • Hot water bottles can be swapped for ice bags.
Article Sources
The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Dealing With Aquariums And Ponds During Power Outages. North Carolina State Veterinary Medicine, 2020