How to Heat Aquarium Water During Cold Weather?

how to heat your aquarium water during periods of intense cold.

If you’ve come this far looking for advice on how to heat your aquarium water, you must have been worried about the health of your fish. Heating the water in an aquarium is not a very difficult process, but if you don’t have the right equipment, you can have several problems when the temperature starts to drop.

Why do my fish stay on the surface… How to heat aquarium water during cold weather?

Below, check out the main tips on how to heat your aquarium water during cold weather.

use a thermostat

The first thing you need to keep in mind when setting up an aquarium is that you will need a thermostat to keep the water warm.

O thermostat It is essential equipment for practically all aquatic environments, with the exception of those where there are species that live in colder waters, for example, kinguios and carp.

This equipment helps to keep the water always warm, as you just need to set it to the temperature your fish need and leave it on inside the aquarium. The thermostat will do all the hard work by itself!

The only thing you will need to understand is what type of thermostat will suit your aquarium. I created an article that will help you find the ideal model,

Generally speaking, the rule you should follow is 5 watts (W) for every 4 liters of water in the aquarium. For example, if you have an aquarium with 75 liters, you will need a thermostat with 100W of power.

Below, I will list some of the most common thermostat models available. If you want to buy them or check out other models, just click on the links:

Is it possible to heat the aquarium water naturally without using a thermostat?

In some more extreme cases, where we cannot buy an emergency thermostat to heat the water, it is possible to use some alternative methods. Below, I will list some of these methods, but I will assure you that they may not work properly, as most recommended is to buy a thermostat.

Use warm water during partial changes

Accomplish partial water changes with slightly warmer water can help you get the temperature you need to keep your fish healthy.

Remember that the temperature needs to be increased slowly! Raising it quickly can be fatal for many species of fish. So, if you choose this method, boil some water and add it to another at room temperature. After that, check if the temperature is a little above the water in your aquarium and pour very slowly to avoid thermal shock.

Fill a bottle with warm water

This method works the same as partial hot water changes, but can be a little more dangerous if you’re not careful.

You can heat some water and add it to a tightly closed pet bottle. Then just leave that bottle floating inside the aquarium for it to do its job.

Of course, this method may not be efficient if you have a very large tank, but it can still help you keep the water a little warmer for the fish anyway.

Just make sure that the water in this bottle doesn’t get too hot so there won’t be big fluctuations in temperature inside the aquarium.

Insulate your aquarium glass

If you’ve managed to warm up your aquarium water a little with any of the above methods, it’s time to try to keep that temperature constant.

A very interesting tip used by aquarists around the world is to insulate the aquarium glass with some type of material that has this function.

If you have Styrofoam at home, you can tape it to the sides of the aquarium to try to keep the water warm. Yes, I know it doesn’t look pretty! But still, in a desperate situation, it can help keep you warm for longer.

Use powerful lights

A lighting system with stronger lights will have the same warming effect as placing your aquarium in direct sunlight. O algae growth it may even be a problem, but you will still be able to save your fish!

Keeping the lights on for 8-10 hours a day will keep an aquarium warm without a thermostat, even more so if we are talking about a small aquarium with a very bright light above it.

Decrease the filter power a little

The gas exchange generated by agitating the surface of the water can cause it to cool very quickly. So, if you can get your fish to an acceptable temperature using some of the methods above, reduce the water flow to the filter a little to avoid this surface agitation.

Just pay attention to the ideal conditions your fish need to live, as some species require rougher waters, while others can live in more peaceful environments.


Heating the aquarium water during cold weather is not a very difficult task, especially if you have done your homework.

Otherwise, you can use some of the methods above. But remember that they are palliative and that during their execution, you will have to purchase a thermostat to avoid temperature fluctuations in the future!

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