Do Guppies Need A Heater? Tips For Maintaining Temperature In Your Tank.

Dec 5, 2020

Do Guppies need a heater?

You can find guppies everywhere—from the bluest waters of the tropics to the sewers of metropolitans. And let’s not forget just about every pet shop in the world. Guppies are incredibly hardy fish that can survive in a wide range of environments. But in reality, what water temperature is ideal for guppies? Are you curious to know?

Let’s find out.

Do Guppies Need A Heater? Here’s What You Want To Know.  

Guppies are natives Caribbean, where the water is always warmer compared to other parts of the world. Thus, your guppies do need a heater—ideally. However, if you live in a tropical region where the temperature never falls below 68 °F (20 °C), your guppies can do without a heater.

But since that’s rarely the case, you need to get your guppies a suitable heater.

What’s The Best Temperature For Guppies?

In nature, guppies mostly live in water bodies with a temperature between 74-82°F (23-27°C).

Thus, it’s best if you replicate the same water temperature for your guppies. This is also the ideal parameter for most aquarium fish. So that’s a win-win for all parties.

As a hardy species, guppies can survive temperature changes and even cold water—but that comes at a cost.

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Why Are Guppies So Colorful – And Why Do Guppies Lose Color?

Can Guppies Live In Cold Water?

Yes. Guppies can live in water as cold as 60 °F (15 °C). But that has a detrimental impact on their health and overall wellbeing. It significantly reduces their health quality and productivity while also shortening their lifespan.

Your guppies can put up a fight in the cold water but will eventually give in to the various disease and stress factors.

Let’s find out how cold water affects guppies.

What Happens To Guppies If You Keep Them In Cold Water?

As hardy as guppies are, wrong water temperature can inflict some serious harm. Besides making them sluggish and stressed most of the time, consistent exposure to cold water will also negatively impact their fertility, immune system, and growth.

Guppies Become Lethargic And Sluggish

Like all cold-blooded beings, guppies need heat to become active.

Thus, if the water is cold, they will not generate enough energy to keep themselves warm—let alone swim around and flaunt those fins.

Guppies Will Breed Less Often

If there’s one thing guppies are famous for, that’s their prolific breeding capabilities. However, if the water is cold, you’ll reduce fewer and fewer guppy fries in the tank.

That’s because guppies strongly prefer warm water to breed.

Guppies Will Stress More 

As a result of a colder, and thus inhospitable environment, your guppies will stress out more. In turn, this can degrade the health by weakening immunity.

The stress can also be a triggering factor for aggression and fights within the tank mates.

Guppies Will Be More Prone Disease

Guppies and cold water is a recipe for diseases. Colder temperatures expose them to several health complications and aggravate the existing ones by manifolds.

Guppies Will Have Slow Growth Rate

One of the most noticeable effects of cold water is that the once lustrous scales will appear duller. But the loss of shine is just symbolic.

Guppies cannot merely thrive in cold water. Their organs will not develop as well they should. As a result, your guppies will face lots of health problems in the future.

The four reasons stated above are enough to answer do guppies need a heater.

But it’s not just cold water that’s harmful to your guppies. Overly warm water can have equally dire consequences.

Let’s have a look.

What Happens If You Overheat Your Guppies?

The general notion is that anything above 85°F (29°C) is considered too hot for guppies. Constant exposure to hot water can reduce fertility, weaken their immune system, and even suffocate guppies.

Here are a few potential harms of overheating your guppies:

Reduced Fertility In Guppies

While guppies need warm water to breed, overheating will reduce sperm count in male guppies. As a result, there will be a general effect on male guppies’ reproductive success.

Weakened Immune System In Guppies 


Just like excessive coldness, overheating can weaken immune levels. A higher level of water temperature is linked with lysozyme overproduction and immunoglobulin M levels in guppies.

Suffocation In Guppies

Hot water has considerably reduced levels of oxygen. Thus, there’s a good chance that guppies will suffocate in an overheated tank.

Suppose you notice your guppies swimming to the surface often or rapidly moving their gills. In that case, it’s a telltale sign that the tank’s oxygen level has depleted.

Do Guppy Fry Need A Heater?

Guppy fries cannot hold body heat for longer periods, given their petite size. Thus, they need warm water to keep their body temperature in check. Hence, the answer to do guppy fry needs a heater is a big yes.

In fact, they need a bit warmer temperature than their parents.

Ideal water temperature for guppy fry: 78°F (25.6°C)

Ideal water temperature for juvenile guppy: 74°F (23.3°C)

Heater Capacity And Tank Size Guide For Guppies

There’s no one specific rule exclusively made for guppies when it comes to determining the heater’s power. It depends mostly on the tank’s size. The rule of thumb is 5 watts for every gallon of water for aquarium fish.

Now, let’s assume the room’s temperature is 70°F. A room temperature is generally defined to be between 68-72°F (20-22°C).

In that case, the ideal heater capacity for a given tank size would be:

Tank SizeHeater Wattage
5 Gallons (19 Liters)                                                   25W                     
10 Gallons (38 Liters) 50W
20 Gallons (76 Liters)             75W
25 Gallons (95 Liters)              100W
40 Gallons (152 Liters)                 150W
50 Gallons (200 Liters)             200W
65 Gallons (250 Liters)            250W
78 Gallons (300 Liters)      300W

What Type Of Heater Is Suitable For Guppies?

All aquarium heaters have the end goal to heat the water, but not all of them have the same mechanism of doing so.

To ascertain what type of heater is best for guppies, you need to consider your tank’s setup first.

Here are the four most common types of heaters:

Substrate Heaters

Substrate heaters feature coils that are attached below the substrate. Once activated, it will keep the water warm.  

The advantage of the substrate heater is that it warms the water uniformly and is not visible. It’s best used for tanks with guppies and live plants.

Hang-On Heaters

Hang-on heaters, also known as HOB heaters, are the most popular as they come cheap and often with starter kits.

With HOBs, the control has to be kept above the waterline. However, these are not great for marine or saltwater tanks as there are risks of electrical shock and corrosion.

Submersible Heater

As the name gives away, submersible heaters need to be completely submerged in the water to function.

These are made of comparatively more durable materials than other heaters.

There are many ways to position your submersible heater, but it best works when positioned vertically or horizontally.

Filter Heater/External Inline Heater

Filter heaters are not visible—thus, not meddling with your tank’s aesthetics. Since these are not visible, they won’t be bearing the brunt of your guppies’ aggression either. However, these are only recommended for bigger tanks.

Suppose you’re confused about what heater to use for your beloved guppies. In that case, I’d recommend the Fluval M Submersible heater as it’s one of the few brands I trust for my fish.

Since it is available in 50-watt, 100-watt, 150-watt, and 200-watt options, you can choose one suitable for your tank size.

Here are a few things that stood out for me:

  • A 3-year warranty
  • Adjustable control dial
  • Computer-calibrated thermostat
  • Sleek and neat design

If you’re looking for a more budget-friendly option, Ehiem Jager Aquarium Thermostat can be the right choice for you.

It comes with even more options: 25-watts, 50-watts, ­75-watts, 125-watts, 150-watts, 200-watts, 250-watts, and 300-watts.

Here are the main perks of this heater:

  • Made with shock-resistant, shatter-proof glass
  • Precise temperature regulation
  • Automatically turns off when the water level dips low
  • Thermo safety control protects against running dry

Whatever heater you buy, just keep in mind that it’s not wise to cut corners. A good heater won’t only keep your fish warm and avert risks of electrocution but also last you many years.

How To Know If The Water Temperature Is Too Hot Or Too Cold For Guppies?

We have already established that both ‘too hot’ and ‘too cold’ water poses risks for guppies. So, here are a few ways to tell if the water temperature is on the extreme side for your guppies:

  • Guppies display rapid gill movement since they’re gasping for air
  • Guppies have lost their appetite
  • Guppies are acting lethargic and sluggish
  • Guppies are swimming frequently towards the surface
  • Guppies are acting hyper

How To Test The Water Temperature For Guppies?

Well, not just exclusive for guppies, but there are two main ways of testing the water temperature:

Using A Thermometer

The most effective and foolproof way of measure water temperature is to check using a thermometer.

Simply dip a thermometer in water for a few minutes, and you’ll get a pretty accurate result.

Most heaters these days come with an inbuilt heater—making it easy to gauge the temperature. Otherwise, a suction thermometer is a good choice too.

Testing With Hand

You can also check the temperature using your hand to see if it’s hot, cold, or lukewarm. However, you won’t get an accurate result, and this is far from reliable. Only resort to this method if you don’t have a thermometer at the time of testing.

Do Guppies Need A Spare Heater?

Given the importance of a heater in guppies and guppy fry’s life, a spare heater is always a good idea.

While you may use it seldom, not having one can cost you dearly.

Conclusion On Do Guppies Need A Heater

Whether or not do guppies need a heater is not a debatable question. As tropical fish, their bodies are wired to thrive in warm water. Thus, the water temperature should be around 74-82°F (23-27°C) for guppies.

If the water is cold, it invites many complications for your guppies—from reduced fertility levels to dull appearance and diseases. Thus, it’s best to invest in reliable water to provide an ideal and stable water temperature for your guppies every time.

Further Readings:

Do Guppies Eat Each Other? Guide on Cannibalism and Guppies

Can Guppies Live in Saltwater? Tips For Keeping Saltwater Guppies Happy

Can Guppies Live in a Bowl? Tips for Happy Guppy

rohit gurung author at urbanfishkeeping

About Rohit Gurung

My never-ending love and fascination with Aquascaping started when I received a red-eared turtle for my 10th birthday.

Apart from researching and writing, I spend hours gazing at my 3 turtles. And yeah, I bask alongside them too.