How to Warm Up a Betta Tank Without a Heater?

Last Updated on October 5, 2020

Are you looking to learn how to warm up a betta tank without a heater? Then, this article is perfect for you!

Betta fish originated from Thailand and spread around Southeast Asia where the climate is of the tropical range. The streams and rice paddies where the betta fish originated from are mostly shallow and let the sunlight to constantly heat the water.

Fish keepers who live in tropical countries need not worry so much about the temperature of their betta fish tank if kept at room temperature. For hobbyists living in colder countries, using a heater for even the coolest betta fish tanks is always advised to keep the water temperature constant.

There are instances however when you will not be able to generate heat such as when the power goes out, if your heater suddenly stops working, or when you are still undecided in buying a heater to test the newest features.

Can betta fish live in cold water?

Being constantly exposed to water with a temperature that is lower than 25°C or 77°F will make the betta sluggish, lose its appetite, and prone to being sick.

Diseases such as fin rot and ich will easily infect a betta in a cold environment. The betta fish’s immune system can not fight off invading microorganisms because the constant exposure to cold temperature makes it prone to disease and ultimately leading to death.

How to warm up betta tank without heater

How warm should a betta tank be?

The habitat where the betta came from in tropical countries of Southeast Asia has a temperature range of 25 to 31.5°Cor 77 to 88.7°F. In an aquarium, betta fish needs a range of 25-27°C or 78-80°F. 

In the wild, a betta fish can transfer location if it detects fluctuations in the temperature. However, it doesn’t have this option in an aquarium.

Related: Can I Add Warm Water to a Fish Tank?

How to warm up a betta tank without a heater?

Here are some things you can do if you can’t provide a heater for your betta fish tank. Be sure to have your aquarium water thermometer at all times to monitor the temperature of your betta fish tank. Make sure the temperature doesn’t fluctuate too much within 8 hours.

  • Place your fish tank in a room that has a heater. Houses in tropical countries will most likely not have a heater due to the natural climate there. Houses in colder countries have a heating system in place. You can set up your fish tank if the room is at 26°C or 80°F.
  • Sunlight will warm a small gallon fish tank if it shines on it directly. The disadvantage of this is that you can’t control how intense and how fast the heat from the sun will increase the temperature. Another problem is that this can promote the growth of algae.
  • Turn on the light of your fish tank. The light will generate heat, however, this might not keep the temperature stable because you will still need to turn it off at night. Fish need the lights off to sleep too.
  • Using hot water placed inside a water bottle can also help increase the tank’s temperature. This isn’t a long-term solution. It is not practical to do. You can do this in case your heater malfunctions and you are waiting for a replacement. 
  • Carefully fill an empty water bottle with hot water. Close it with its cap and let it float on the surface of your betta fish tank. You will need constant monitoring to make sure that the temperature fluctuation is not drastic. Replace the hot water as needed.
  • Insulating your fish tank will also conserve the heat. You should do this after doing one method previously described. You can cover your fish tank with a blanket to keep the heat in. Avoid covering the entire opening to allow air exchange. 

Related: What Do Betta Fish Like in Their Tank?

What happens if betta water is too hot?

A lot of problems will happen if your betta fish’s tank exceeds 32°C or 90°F. It will be harmful to your betta fish and the beneficial bacteria in the fish tank.

A temperature that is too high will increase the betta fish’s metabolism and this will shorten their lifespan. This increases its metabolic processes such as breathing. Breathing fast through its gills will directly consume the oxygen from the water column. If breathing air directly is done through its labyrinth organ again and again, then this will cause exhaustion to your betta because it will constantly gulp for air at the surface of the water. 

Add to this the fact that warmer water contains less oxygen. The beneficial bacteria in your betta fish’s tank need oxygen to break down ammonia. If oxygen drops because of the increase in temperature then the ammonia levels may spike. These beneficial bacteria die at 35°C or 95°F and this will surely lead to an ammonia spike. Ammonia is a fish killer. It will burn your fish’s gills and internal organs.

What to do if you notice your betta fish’s tank water temperature is too hot

There may be days when it will be a lot hotter than normal. Check the temperature of your aquarium water and do the following.

  • Turn off the lights of your aquarium.
  • Block any sunlight that may shine on your tank.
  • Remove the tank’s cover/lid and replace it with a net to avoid any fish jumping out.
  • Direct an electric fan’s airflow towards the surface of your betta fish tank.
  • You can float an ice pack.

Make sure you are not decreasing the water temperature too fast because it will shock your fish. 1 degree Celsius or 2 degrees Fahrenheit every 8 hours is enough. Note the temperature and keep it stable if you reach the normal range.


The temperature of aquarium water plays a very important role in maintaining the health of your betta fish so knowing how to warm up a betta tank without a heater is a skill you should learn. Betta fish thrive in the tropical temperature range and we should ensure that we keep this constant in our aquariums.

We hope this article sheds light on how to warm up a betta tank without a heater to help betta fish be comfortable and healthy.

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