How To Keep A Fish Tank Warm Without A Heater Using 6 Tips

How To Keep A Fish Tank Warm Without A Heater
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Fish require support to retain ideal body temperatures because they can’t generate body heat by themselves. If you have a damaged heater, a power cut, or can’t afford an aquarium heater, this could be an issue. 


It pays to know how to keep a fish tank warm without using a heater. 

The water temperature greatly influences a fish’s health. It affects ammonia or oxygen levels, fish digestion, immunological function, and the population of bacteria and algae in the fish tank.

Therefore, read on to find out how to keep your fish warm without an aquarium water heater.

Why You May Need to Make a Fish Tank Warm Without a Heater

Why would anyone bother to learn how to make a fish tank warm without using a submersible aquarium heater? Let’s see.

  1. Power outage: How common they’re and how long they last. You may need a backup plan whenever a power outage occurs.
  2. Heater failures/replacements: Keeping a tropical fish tank cold while awaiting a heater replacement can cause significant damage.
  3. Housing tropical fish: People in ordinarily warm places don’t usually have heaters. But during unusually cold periods, when rapid water temperature changes occur, you may need to make your fish tank warm.
  4. Establishing a quarantine tank: You’ll need to do this, especially if it’s an unforeseen occurrence (diseased or injured fish) and there’s no funding for an extra heater.
  5. Choosing a wireless system: Having a cordless arrangement can bring aquascaping in a nano tank to another level, and it’s a valid option if you desire it.

Ways to Keep a Warm Fish Tank Without Using a Heater

Below are some of the best ways to ensure your fish tank stays warm without aquarium heaters:

1. Get a Small Tank

If this is the first time you’re trying an aquarium setup without a heater, nano tanks are ideal. They heat up quickly and maintain a consistent temperature with little or no stress to you.

Get a Small Tank

The small fish tank may grow colder faster in extremely cold conditions or during a power outage. Still, it’s easier to control damages in a small tank than in the big one.

2. Raise the Temperature Inside Your Residence

This may sound like a no-brainer, yet many people are adamant about the temperatures that our thermostats are set at.

When managing the aquarium temperature without using a heater, try to keep your room temperature slightly above 78 degrees Fahrenheit.

Raise the Temperature Inside Your Residence
Modern Programming Thermostat

This step may be sufficient to bring the temperature of the water to a tolerable level for fish in a nano tank.

3. Keep the Aquarium Close to a Heated Place

Almost every home possesses some warm spots, and you could use these if you’re not using a heater. Keeping the aquarium inside the warm portion of the room could raise the water temperature to a conducive level for your fish.

Keep the Aquarium Close to a Heated Place

The following are a few things to consider when picking where to place the aquarium:

  • Relocate the aquarium to the higher floor (in a multi-story house): This could make a temperature variation of a degree or two since upper floors are often warmer.
  • Avoid drafty areas: These areas are usually cold. Although the cooler airflow may not appear in large amounts, it may drop the temperature in your tank, thereby negating your efforts.
  • The sunniest site is best: Find a spot in your house where the aquarium could acquire at least 7 hours of direct sunlight per day, and you’ll be astonished at how quickly aquarium water could warm up with no further help.

Have a few algae-control products in your possession if you’re taking the sunniest-sunshine route, as growth in algae could spike when there’s much sunlight hitting the room.

4. Water Changes Should Be Made With Warm Water

Warm water changes could help you adjust your tank’s water to the appropriate temperature level without utilizing a fish tank heater.

Water Changes Should Be Made With Warm Water

Of course, you must gradually raise the temperature as the fish will suffer if the temperature rises too fast.

In addition, you can combine room temperature water with some amount of boiled water. However, never pour boiling water straight into your aquarium (whether the tank is empty or not).

5. Insulate the Walls of the Tank’s Glass

After you’ve gotten your tank’s water temperature level to an appropriate degree for the aquatic pet you’re keeping, shielding your tank’s glass walls would be a good idea.

While applying styrofoam to the inner and outer layers of the tank isn’t the most pleasing option, using an insulation material or tin foil to the tank’s walls is a close second.

Insulate the Walls of the Tank's Glass

This approach won’t stop the water temperature from dropping, but it’ll reduce the frequency you need to change the water.

6. Warm the Water in Your Tank Gradually

Whenever you’re attempting to keep a fish tank warm, you can slowly heat the water in the tank. However, it’s only advocated as a temporary solution.

You can temporarily warm the water in your fish tank by placing a hot water bottle or a hot water container in your fish tank. Then, let it remain on top of the water until the tank water becomes warm.

Warm the Water in Your Tank Gradually

To keep things in context, if you want your tank to be 80 degrees Fahrenheit, set the temperature of the hot water bottle or a hot water container to 120 degrees Fahrenheit.

Since it may allow for some very severe changes in the temperature, it’s not good to try it with delicate fish. Slowly cooling water is less damaging than sudden temperature changes.

Add-Ons That Make It Easier to Retain Warmth in a Fish Tank Without an Aquarium Heater

If you’re still tinkering with a heater-free aquarium arrangement, you can include a few components into your tank to keep it warm.

1. Use an Aquarium Lid to Cover Your Fish Tank

Use an Aquarium Lid to Cover Your Fish Tank

When keeping an aquarium warm without a heater, employing a cover that limits direct interaction between your fish tank’s surface and cold air circulation is easy.

Any tank cover would trap heat and enhance your other warming efforts far more effectively. In addition, most fish tanks work well with easily detachable lids, allowing easy feeding, upkeep, and maintenance.

Although a lid could decrease the quantity of oxygen in the water, an air pump and air stone can help to improve oxygenation.

2. Regularly Check the Water’s Temperature With a Thermometer

Regularly Check the Water's Temperature With a Thermometer

A thermometer can assist you in keeping track of the warmth in your fish tanks and determine how effective (or ineffective) your warming methods are.

Retain freshwater testing kits on hand to monitor how the temperature affects the overall water parameters in your tank.

3. Use Brighter Lights

Use Brighter Lights

Placing the fish tank under sunlight or using a lighting setup with bright lights could have the same warming effect. This way, you’ll be able to manage the amount of light your fish tank receives. In this situation, algae growth may still be a problem, but you can take steps to help reduce it.

Even if we’re talking about a nano aquarium, leaving the aquarium lights functioning for a longer period will readily keep it warm without a heater.

4. Use a Non-Energy-Efficient Filter

One of the most out-of-the-box tactics you may consider is using a non-energy-efficient filter to leave a fish tank warmer without a heater. Less efficient filter cartridges run hot since they consume so much extra energy. The filter’s engine can quickly heat the water in the tank. You may have hassle-free warm aquarium water when you combine this with an insulating add-on like a heating pad.

5. Use a Heating Pad (Quite Suitable for Smaller Fishbowls)

Use a Heating Pad

Heating pads are designed to warm vivarium settings, but you could also use them to heat water in a small fishbowl. To minimize hot areas and glass cracking, you’ll need to add an interlayer between the heating pad and the bowl’s bottom Note that since glass is a poor heat conductor, this addition is one of the least effective.

6. If It’s an Emergency, Bring Blankets and Heavy Towels

You’re likely not going to utilize this “add-on” if you’re looking for a long-term solution to keep a fish tank warmer without a heater. But in an emergency, a heavy blanket or thick towel is the finest insulating covering you can employ.

In the event of a power loss, a blanket or thick blanket draped around the tank’s glass panels can help regulate the temperature and allow for a gradual cool-down. 

The Ideal Water Temperature in a Fish Tank

The most comfortable temperature for fish is in the range of 76 to 80 degrees Fahrenheit. Therefore, this temperature mode is suitable for most inhabitants of the aquarium.

Allowing the water heating level to rise above 80 degrees and fall below 76 might be dangerous for fish health. Exceptions are situations where such indicators are suitable for the normal life of specific species.

How Sensitive Are Fish to Temperature Changes?

Fish feel the slightest change in water temperature. Aquarium fish are usually all tropical species, which means they’re accustomed to living in warm water with a constant temperature. 

In the event of a sudden change, if they don’t die, they’ll experience significant stress and may get a contagious disease due to a weakened immune system.

Fish that live in a temperate climate are much more resilient. For example, cold-water fish like goldfish can live at temperatures as low as 41 degrees Fahrenheit and more than 86 degrees Fahrenheit. However, exposure to such temperatures for an extended period is harmful to them.

Are There Fish That Tolerate Extreme Waters?

Several species can temporarily live in hot water. For example, some species of marine fish that live in the Death Valley can tolerate up to 113°F, and some tilapia fish swim in hot springs with temperatures more than that. 

But not all of these fish can live long in such water because the protein in their blood starts to coagulate. 

However, there are more fish that can live in icy water. For example, at both poles, there are fish that produce a kind of antifreeze in their blood, which allows them to live in water with a temperature below zero.

Fun Fact: We have been talking about betta, tetra, shrimp, and other fish species with regard to water temperature. But what about goldfish? The best way to introduce goldfish into our topic is to read our article on Goldfish Water: Types And Conditions For Your Pet to get you started!

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Frequently Asked Questions

How long could a fish go without a heated fish tank?

This depends on the type of fish you own and your area of residence. If you reside within a tropical region with year-round temperatures of roughly 80°F and own a tropical fish such as a Betta fish, you won’t need a heater in your Betta fish tank for a couple of years. 

Does my aquarium heater size matter?

Yes, an aquarium heater matters. Determine the aquarium heater wattage per gallon and select an appropriate aquarium heater size for your tank. For instance, if you need to raise the temperature of a 20-gallon water tank by 18 degrees Fahrenheit, you’ll need to use a 75-watt heater at the proper temperature.


Fish are adorable pets that require more care than other pets because they live in a completely different environment: water. Unfortunately, the temperature of the water can rapidly change from hot to cold, presenting complications for your fish. As a result, keeping the fish tank temperature stable is a crucial factor for all fish owners.

You may encounter problems such as a power outage, a heater malfunction, or that you have never lived with a heater before. In these circumstances, you’ll have to manually heat the tank.

So, you may keep a fish tank warm without using a heater by raising the temperature in your home, insulating the tank’s glass walls, putting your aquarium near a heated area, and more!

Last Updated: July 13, 2022