How to Keep a Fish Tank Warm without a Heater

If you are wondering why you may need to keep a fish tank warm without a heater, there are a few reasons. For starters, you may have had to set up a tank in an emergency, for example, to separate a fish that is sick or aggressive from the rest of the tank.

However, keeping a tank warm without a heater can be great for hardy fish like Comet Goldfish. It saves power, and resources, and is less hassle to set up. A naturally heated tank, however, can work for a variety of fish species and is a great option if you want something easy and natural. Read on to find out how to make it work.  

Why May You Need To Keep A Fish Tank Warm Without A Heater? 

Outside of emergencies, there are many reasons you may deliberately choose an unheated tank, such as cost, and wanting to minimize wires and cables or the risk of electricity near water (for example, if you set up your tank for children). Or, you may simply desire a cleaner-looking setup. Tropical aquariums also contribute to up to 12.5% of CO2 emissions in some countries, so you may also have environmental concerns. 

Generally, most experts recommend keeping a tank with a heater. In addition, low temperatures can affect the diversity of bacteria in your aquarium filter, vital for keeping the water clean. 

Either way, this guide will show you how to keep a heater-less fish tank as an option – because even though heated tanks tend to be the norm, it’s always possible to do something different provided you have done your research. Read on for more info. 

Ways To Keep Your Tank Warm Without A Heater: 

Keep It in a Warm Room

It goes without saying, but paying attention to the general ambiance of a room is a good way to ensure your tank stays warm. Is the tank positioned somewhere sheltered, or is it in line with draughts? 

Some kinds of rooms are really good for keeping a warm general temperature. They tend to be bright and sunlit with lots of glass. If you are lucky enough to have a greenhouse or conservatory this can be a great place for a fish tank due to how warm they can become. 

Otherwise, rooms that are at the top of the house, with lots of soft furnishings and thick walls tend to be warmer than average. 

Insulate the Tank 

Insulating the tank is one of the most surefire ways you can use to ensure it stays warm without a heater. The only difficulty is many insulating materials such as Styrofoam and even silver insulation can look relatively ugly next to the beautiful interior of your tank. Therefore, you may be able to spruce things up a bit by adding an extra layer over your insulation. 

For example, if you have insulation on the back and both sides of your ank you can then cover these with wood panels to make your tank more aesthetically pleasing. 

How Does Insulation Work?

Insulation is any material that stops more heat from escaping. It generally does this by blocking the exchange of heat from the inside of the tank to the air outside. Your tank will lose what to the air outside if it is warmer, so keeping your tank water close to room temperature – or room temperature close to your tank water, also helps even if you do add insulation. 

What Is Insulation Made From? 

Insulation for fish tanks can be made of many materials and not all of them are sold specifically for tank purposes. Styrofoam or other forms of foam are a popular choice. Polystyrene insulation is similar and is sold commercially as a DIY material, but felt and blankets can keep a tank warm in winter at a pinch too. 

Use A Powerful LED Light 

All lights also give off some energy in the form of heat, but how much depends on the individual light in question. Some LED bulbs that are commonly used to light aquariums are also very hot, so if you have one of these with a proportionately small tank, it can heat up the surface of the water quite quickly and prevent your tank from getting too cold.

Adjust the Surrounding Environment

You may have done everything you can to ensure your tank is in a location where it is easy to keep warm, but if you’re still worried about the temperature of the water, you may need to adjust the surroundings further. For example, if you have a radiator near the tank, you can turn it up, or even a portable electric heater as is common in some houses. 

You may find the behavior of your fish changes with temperature. In some studies, higher temperature makes fish more active. Conversely, if your temperature gets too low, fish may become lethargic. Either way, if you don’t have a heater, your tank may be more prone to fluctuations so be careful if it is near any external heat sources as the heat these provide will be less constant. Always observe your fish’s behavior closely. 

Start With Warm Water

It might sound obvious, but if you start your tank off with the warmest water possible for the kind of fish that you want to keep, you will be able to give yourself an edge in keeping it warm. 

This is best for fish that can tolerate both warmer and cooler temperatures such as Danios, Mollies, Platies, and Guppies, and are ok with slight fluctuations. Zebra Danios can in fact live in water of 70 F or 21 C, which is possible to maintain without a heater depending on where you live and the room your tank is in.

Use Cold-Water, Hardy Fish

Of course the qualifier ‘warm’ is relative. This is because what’s warm to one fish species may be unbearably hot to another and what’s cold to one may be just right for a second. You will be surprised at just how many species of ornamental fish there are that are hardy and can thrive in quite cool conditions. 

For example, many first-time fishkeepers see Guppies only as tropical fish. Of course, this isn’t wrong, and this is why you generally see them labeled as such in fish and aquatics shops. 

However, these livebearers are hardy and they can survive in temperatures at the lower end of their range, around 23 C, quite easily. As this is room temperature in many houses, it’s, therefore, easier than you may think to keep a Guppy tank without a heater.

Which Goldfish Varieties Can Tolerate Cooler Temperatures? 

However, be very careful as to which variety of Goldfish you are getting. Some of the more delicate Goldfish, such as the Bubble Eye Goldfish, may not require temperatures the same as tropical fish but they nevertheless are far more easily stressed by cold, as well as by rapid fluctuations in temperature, than their hardier counterparts like the comet Goldfish.

Final Thoughts

Ultimate it can be easier than it looks to keep a fish tank without a heater. However, please ensure that you are careful and diligent with the upkeep of your tank, monitoring the water temperature (a tank thermometer is great for this!) to ensure there is not too much strain on your fish. In this way, with some planning, it’s easy to keep a heater-less tank that actually thrives.


Here few Question that frequently asked:

What do I do if my tank temperature gets too low?

You may have been monitoring your tank temperature closely with a tank thermometer when you suddenly see it plummet. Stay calm and look for the source of the cold, for example, if you have had an unnaturally cold winter, simply move the tank near an electric heater. 

Otherwise, you can warm the tank temperature by doing a water change and adding water that is one degree warmer. If you do this on a frequent basis such as daily, you will soon be able to raise the temperature again. 

How can I save my fish if they get stressed from the cold?

If your fish are a hardy species, it’s easy to help them recover by simply raising the tank temperature slowly.
Temperature fluctuation and related stress can reduce Goldfish lifespan. However, if your fish have got too cold, you can rebuild their strength by feeding additional protein and keeping water parameters stable.

What types of tanks are better suited to colder water? 

As we mentioned above, a Goldfish tank is one of the best suited to Coldwater conditions and if you keep hardy Goldfish like the fantail Goldfish or comet Goldfish you will find you don’t even need a heater.

Bear in mind that tropical tank setups like an Amazonian tank or betta fish tank absolutely cannot work without a heater. On the other hand, a Nano fish tank with hardy, subtropical schooling fish can be a good option if you have little space.

Joseph P-Little, the Content Manager at Cartwisely, is a seasoned wordsmith and content strategist. He's dedicated to helping brands reach their full potential through engaging, creative content. With a talent for storytelling and a commitment to excellence, Joseph transforms ideas into impactful narratives.

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