Do Guppies Need A Heater?(Complete Guide 2021) is supported by our readers. When you buy through links on our site, we may earn a commission.

Guppies are tropical fish known for their bright colors and larger-than-life personalities. They are an incredibly common fish in the aquarium hobby and are the favorites of many hobbyists around the world.

If you’ve been looking into adopting a school of guppies, you might be wondering how to properly care for them. Do guppies need a heater to survive? If so, how many watts should their heater be? What happens when the water temperature changes too rapidly or gets too high or low?

The good news is that we’ve got the answers to all those questions and more — and we’re going to share them with you in this in-depth article.

Do Guppies Need A Heater?

Guppies are tropical fish and as such, they definitely need a heater. In order for them to live a long, happy life their bodies need to stay warm. Having a heater in your guppy tank will help ensure that your water is always at the best temperature for your fish.

Ideal Water Temperature for Guppies

While guppies do need warm water to thrive, they can’t just be thrown into any warm water. Their water needs to be within a certain temperature range to be suitable.

Guppies need to be kept at a temperature that falls within the range of 72-82 degrees Fahrenheit. They can be kept at temperatures slightly higher or slightly lower without much concern, though. If kept at higher or lower temperatures for too long, though, their immune systems can become compromised, making them susceptible to illness and disease.

To ensure that your water is at the correct water temperature, keep a thermometer in the tank. Put it at the opposite end of where your heater is placed. This allows you to monitor how well your heater is heating the water.

A good rule of thumb is that if your water reads at a comfortable temperature when the thermometer is at the opposite end of the tank, your water is likely heated evenly.

Credit: towert7

What Happens If The Water Gets Too Cold?

Water that is too cold can be disastrous for your guppies. You’ll know when the water has become too cold when your guppies start to show the effects of the temperature.

Symptoms of this include:

  • Swimming sluggishly
  • Acting lethargic
  • Appetite loss

They start to display these symptoms because they are cold-blooded so when the water gets too cold, so does the water temperature of their bodies, which makes them sluggish and slow.

It also causes their body stress, which leads to a lack of appetite as it does in most other creatures on Earth. Paired with the resulting lethargy, appetite loss will weaken their immune system.

When this happens, they’ll start spending more time at the bottom of the tank. If you happen to have more territorial fish that dwell near the bottom of your tank, your guppies can get picked on and injured.

If you don’t bring the water temperature up when it drops too low, your guppy is more likely to suffer from illness and disease thanks to the weakened state of their immune system. Diseases such as dropsy, fin rot, and swim bladder disease are common in fish that live in water that is too cold.

What Happens If The Water Gets Too Hot

Although it’s less likely, your aquarium water getting too hot also poses a risk to your guppies. When the water starts to get too warm, your fish will begin swimming erratically, which is what happens as your fish’s energy levels increase due to the drastic temperature rise.

The energy increase seems like it would be a positive thing but it’s actually a negative. The energy increase is going to stress them out the same amount as if the water were to get too cold. Their immune system can and will get worn down, leaving them vulnerable to health issues.

Luckily, though, it’s much easier to cool a tank down than it is to heat it up. To cool a tank down quickly, you can just add a cup or two of conditioned tap water that is cooler than the water in your tank. Or you could take the lid off the aquarium if you have one on. For long-term cooling, you could consider using a small fan!

How to Set Up a Heater for Guppies 

When setting up your heater, try to place it as close to the filter as possible. This helps the heat from the heater to be dispersed throughout the tank, as the warm water is pushed around the tank by the current of the filter. If you place your heater too far from the filter, you could end up with cold spots within your tank.

Sometimes you might need more than one heater in a tank – for example, if you have a very large tank fish that require particularly warm water, or heaters that are too low of wattage to achieve the desired water temperature on their own.

In cases like this, place one heater on the end with the filter and the other on the opposite end.

What Type of Aquarium Heater Can You Use for Your Guppy Tank? 

Hang-on Back

Hang-on back (HOB) heaters are the most common type of heater across the aquarium hobby. They are affordable and can be purchased as part of a kit of own their own.

This type of heaters hangs on the side of your aquarium, usually using a set of suction cups. The heating element is contained in glass tubing, which is the part of the heater that is inside of the water.

(HOB) heater is ideal for freshwater aquariums, like the one required for guppies, but shouldn’t be used for saltwater.


Submersible heaters are installed below the waterline, meaning that the entire heater is below the surface. It’s made of durable glass or plastic.

It can be positioned within the aquarium any way you choose. You could have it lying down on the bottom of the tank, leaning against a corner of the tank, or standing straight up and down.

For the best results, consider positioning this heater so that it’s on a horizontal or vertical angle, as these positions allow the heater’s internal thermostat to read the temperature of the water accurately.


Substrate heaters are installed below the substrate of your tank. It’s a great option if you have both live plants and fish in one aquarium. This kind of heater works by heating the gravel, which then heaters the water.

The best part of this type of filter is that you’re almost guaranteed to get an even temperature, as the heater stretches across the bottom of most of the aquarium. It’s also buried beneath the substrate, which does wonders for the appearance of your aquarium.

Heaters are a wonderful piece of technology. Their invention meant that fish enthusiasts could start keeping guppies in their homes without worrying about their health or safety. Today, heaters are very sophisticated and versatile.

Since your guppies need a heater, it’s important to ensure that you have a heater that is big enough for your tank and that is safe for all the inhabitants. You can choose between a few different types of heaters, as well as various sizes, so it should be relatively easy to find the best one for your set-up.

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Jeff Colt

Jeff Colt

Hello, I'm Jeff- an aquarium enthusiast with over 25 years of experience caring for a wide array of tropical fish, including koi, goldfish bettas, cichlids and more! For me: Aquariums are like jello - there's always room for more!

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