How to Keep A Betta Warm

How to Keep A Betta Warm Without A Heater

Betta fish is a species of tropical fish that must live in water between 78-82 degrees Fahrenheit. They become inactive and prone to many diseases if kept at too low of a temperature. A sad, lethargic little fish will perk up as soon as they get enough warmth.

Let’s suppose you don’t have access to an aquarium heater for one reason or another. Luckily, you can still keep your little buddy happy and healthy without one. In order to keep the tank heated, you will need one or more of the following methods. You can heat the room, use sunlight or another light, a low-quality filter, boiled water, insulation, or temporary methods meant for a power outage.

Heated Room

A heated room is the most effective method of heating a tank aside from an aquarium heater. The room will have to be very warm, warmer than 80 degrees. In some areas of the world, this is hardly an issue, but in cooler climates, it can be quite difficult.

The room would have to have a consistent heater. One of the main benefits of a heater is the fact that it keeps the water at a stable temperature. Temperature fluctuations stress out bettas and stress has a serious, negative impact on the immune system of bettas. When stressed, the immune system weakens and leaves your betta open to illness. Some fluctuation is acceptable, but if it fluctuates more than 1-2 degrees Fahrenheit per hour, your betta could become stressed.

Central heating or heating units installed in just one room would work. The betta could also live in a room that is already very warm, which would help save money. Most houses have different temperatures throughout them, with some areas being cold and others being warm. If the warm areas can keep water between 78 to 82 degrees, then your betta will thrive.

The main problem with heated rooms that are not mechanically heated is they often lose heat overnight. Bettas still need warm water, even at night, so rooms that cool down overnight will not work. Heating the room and keeping it warm with central heating or a smaller unit is the most effective method.


As we all know, you can’t leave a popsicle out in the sun because it will melt. Similarly, water kept in direct sunlight will heat up more than other water around it. This is the primary reason that lakes and ponds are warm on the surface but have cold water underneath.

It is possible to keep a betta in sunlight to heat the container, but there are two primary issues with this. The first is that your betta may overheat and boil, and the temperature will likely fluctuate. The second is that the heat will be lost during the night, and your fish may become sick.

You will have to constantly monitor your aquarium temperature since it will be prone to change. This method is variable and can vary day to day and requires more work and maintenance than most other methods.

If you have an aquarium lid, you may be able to heat your betta’s water with a submersible aquarium light. No mechanical work is 100% efficient because some energy is always lost as heat energy. Therefore, aquarium lights give off heat as well. If you have a lid, the heat generated by the light may be enough to heat your aquarium. A submersible light is not necessary, but it will heat your aquarium even more.

The main issue with this method is that betta cannot have a light on at night. Fish need a distinct day and night cycle, so they know when to sleep. It is possible to change the light to a dim blue, but the fish will be healthier with a period of pure darkness. Additionally, excess sunlight and regular light can lead to massive algae blooms.

Low Quality Filter

As previously mentioned, all mechanical objects generate heat, no matter how efficient they are. In this case, you will want a very inefficient machine. A low quality, an inefficient filter will generate a great deal of heat. Since the aquarium water is constantly passing through the filter, it will be evenly heated.

Additionally, the filter is constantly on and present, unlike a light, sunlight, or heated room. The heater may cause some temperature fluctuations and may raise the temperature over time, so it is necessary to monitor the temperature closely.

The two main issues with this method is the fact that the filter is inefficient, and the heating is inconsistent. Since the filter is inefficient, you will likely have to use a filter meant for a larger tank. You will likely have to try out several different filters in order to get one that heats up your tank properly.

You also need to ensure the filter keeps the water at a consistent temperature. Since the filter is lower quality, it may vary inefficiently throughout the day, causing temperature fluctuations. Since you will likely have to try different filters, be sure to keep the box and receipt!

Boiled Water

This method requires constant care and monitoring. This is not an effective long-term method but is a very effective short term. Use this method if the power goes out, your heater breaks, or you’re waiting a few days for a heater to come in.

For this method, you will need boiling water and a container that can safely hold boiling water. Since most food-safe objects are also aquarium safe, glass and porcelain cups are good options. There may be some issue with certain dish soaps used, so rinse them with dechlorinated water before use.

For this method, you should first fill the cup, bowl, or container halfway with boiling water. Next, ensure there is nothing to weigh down one side of the container more than the other. Place the container of water into the top of your aquarium and make sure it doesn’t tip. Keep it away from the sides of the aquarium, as you don’t want it to squish you little friend.

Closely monitor the temperature change, and make sure the change isn’t more than 2 degrees per hour. Keeping the temperature stable is the most difficult part of this process, so you will have to frequently remove and replace the container.


Insulating your aquarium may not keep enough heat on its own, but you can combine it with any of the above methods. There are many ways to insulate your aquarium, depending on how permanent you want it to be.

For example, if the insulation is temporary, for just a few hours, a blanket should do the trick. Wrap the blanket around the sides and top of the aquarium but leave room for airflow. Avoid getting the blanket into the water.

Other methods include placing Styrofoam around the whole aquarium or other insulation. For example, you can try to replicate the method used to ship fish. First, make a Styrofoam container around the aquarium, then place a heat pack inside. You can use shipping heat packs, but reusable ones also work, since you will be there to recharge them.

Unlike the other options, insulation can be a permanent solution with little variance in temperature. The best permanent option is to add insulation to the sides and back of the aquarium. Expanding foam attic insulation, like Great Stuff, can be extremely adhesive and can stick to glass, but other brands are still good options. You can spray this across the outside of the aquarium. Try to keep it an inch or thicker to maximize heat retention. This still leaves the top and front uncovered, but you can cover these with temporary insulation. You will then still be able to view your fish and do tank maintenance when you want.

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