Do Guppies Need A Heater? (Temperature Guide & More)

Do guppies need a heater? In this article, you’re going to find out whether a heater is necessary for your tank as well as a lot more valuable information!

As well as learning whether guppies need a heater or not, you’ll also learn the following:

  • What happens when the water gets too hot or cold.
  • What temperature guppies need to survive (and more importantly thrive).
  • How long they can survive without a heater.
  • What happens if the temperature changes rapidly.
  • Where to place your heater.
  • What size heater to put in your tank.

So keep reading to find out!

What Temperature Do Guppies Need?

Guppies need to be kept in water between 74-82°F (23-28°C). While they can be kept in temperatures a little bit lower and a little bit higher, it won’t be the ideal temperature for them, and it could compromise their immune system, making them more susceptible to illness.

It’s important to know this to understand whether guppies need a heater or not.

So, Do Guppies Need A Heater?

YES, you should be putting your guppies in a tank that contains a heater! And it’s not just because the water needs to stay between 74-82°F. It’s also because the temperature needs to stay consistent as well.

If the temperature fluctuates too much then your guppy can suffer from a whole range of problems that could be life-threatening.

The only way you’re going to be able to maintain a constant temperature is by using a heater. Even if the temperature where you live is constantly hot, it may not be the case for your aquarium.

For example, a breeze or a couple of cold days will dramatically drop the temperature in your tank. And water takes a lot longer to heat up than the air around it.

Heater Watt Size Guide

If you’re going to get a heater, then you’ll need to make sure you get the right size wattage for it. Here’s a helpful guide to let you know the different wattage you’ll need, depending on what size your tank is.

Tank SizeWatts
5 Gallons / 22 Liters75 Watts
10 Gallons / 45 Liters75 Watts
15 Gallons / 68 Liters125 Watts
20 Gallons / 90 Liters150 Watts
25 Gallons / 113 Liters200 Watts
40 Gallons / 181 Liters300 Watts
50 Gallons / 220 Liters2 x 200 Watts
75 Gallons / 295 Liters2 x 300 Watts

If you follow this guide you’ll always be safe in the knowledge that you’ve got the right size heater for your guppies tank!

(Find out whether guppies need a filter.)

Recommended Heater

If you don’t have a heater then I recommend the Fluval M Series Heaters. While they’re not the cheapest on the market, they’re the ones I use in my fish tank with great results. Fluval is an extremely trustworthy brand, so you won’t have to worry about them breaking or killing your fish.

Where Should You Place The Heater?

When placing your heater, you should try to keep it as close to the filter as possible. The filter is going to help circulate warm water throughout the tank, which means the temperature will be evenly distributed.

If you don’t place it near the filter, you may end up with one side of the tank warmer than the other.

In some cases, you’ll need to have two or more heaters in the tank (for bigger tanks.) When this is the case, you should place one heater by the filter, and another heater on the opposite side to the first, to help distribute heat evenly.

(Find out whether guppies need an air bubbler.)

What Happens If The Water Gets Too Cold?

If you don’t heat the tank and the water becomes too cold, it can become disastrous for your guppies.

The first sign of a temperature drop affecting your guppies is that they’ll appear sluggish and lethargic. This is because they’re cold-blooded, so their body temperature will match their environment.

This stress on their body also makes it highly likely that they won’t want to eat, which will further weaken their immune system.

At this point, they’ll often start to swim closer to the bottom of the tank. If you have territorial fish there, then it could cause trouble and result in your guppies being attacked.

If the temperature doesn’t rise, with a weakened immune system, it’s much more likely that your guppy will end up suffering from an illness or disease. Fin rot, swim bladder disease, and dropsy, are all going to be a lot more common (and far more likely to become fatal).

What Happens If The Water Gets Too Hot

It’s not just cold water you should worry about but hot water as well. (Although the chances of the tank overheating are less likely).

If your tank does get too hot though, you may notice that your guppies will start swimming erratically, and darting around. This is because they’ll have more energy they’ll need to expend.

While this seems like a positive in fact, it’s going to have disastrous effects on them. It’s going to stress them out massively, weakening their immune system and increasing their risk of becoming sick.

Fortunately, though it’s a lot easier to cool down a tank then it is to heat it up. You can just add more conditioned cool water to the tank (not too much), take the lid of the aquarium off, or just have a fan blow over it!

What Happens If The Temperature Changes Too Suddenly?

If you’re keeping your guppies without a heater, then a sudden drop in temperature is most likely to happen, and it’s also going to be the most dangerous thing out of the three.

When the temperature drops suddenly, there are a few things that can end up happening.

Temperature Shock

Temperature shock is when your guppies go into shock due to a drastic temperature change. It’s most likely to happen when you’re changing the water, but it can happen any time you don’t have a heater in your tank.

If your guppies go into temperature shock then they can die in a matter of minutes. And if they don’t die they could go into a coma which will cause permanent damage to them.

Respiratory Problems

As well as temperature shock, they’re a lot more likely to suffer from respiratory problems as well. This is a lot more likely to happen if the temperature rises too much (which can happen if you’re relying on outside sources to keep your tank warm.)

When the water gets too hot, it loses oxygen, making it much harder for your guppies to breathe. If left too long, this will eventually become fatal.

(Find out whether guppies need light.)

Don’t Rely On The Heater To Tell The Temperature

Lastly, most heaters will tell you what temperature they’re at, but you shouldn’t rely on this only. You should also use a thermometer to make sure the temperature in your tank stays consistent. I use the Marina Floating Thermometer because it’s cheap and reliable!

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Do Guppy Fry Need A Heater?

Yes, just like guppies, guppy fry are going to need a heater to keep warm as well. The heater for your guppy fry should be set between 76-80°F.

What Temperature Can Guppies Tolerate?

While you should never let them live in such temperature, guppies can tolerate temperatures as low as 70°F. An survive for a short period in temperatures as low as 60°F


Now you know that guppies do need heaters, and you should be armed with all the knowledge you need.

The main points to remember are that you shouldn’t let the water become too hot or too cold. And you definitely shouldn’t let the temperature in the tank change too drastically!

If you’re going to place a heater in your tank then you should choose a reliable one such as the Fluval M Series.

And when you need more than one heater in the tank place one by the filter, and one on the opposite side of the tank to evenly disperse the heat.

Lastly, don’t just rely on your tanks heater to let you know what the temperature is, you should also add a thermometer!

If you liked this article, make sure you check out the rest of the website! And if you have any more questions you can ask them in the Q&A Section!