Do Guppies Need a Heater to Survive?

As a prospective guppy owner, do you need to buy a heater for them? Will they die without a heater? Well, from personal experience, I can definitely say that guppies need a heater to thrive.

While they may not die without one, they’ll become sick and their lifespan will drop significantly. Assuming you’re not a fan of sick, dying guppies, I recommend getting a heater for your aquarium.

There’s only one way you can avoid buying a heater – living in a tropical climate. Guppies need a constant temperature of around 68 F (20 C). Can you provide that? If no, then a heater it is!

How Powerful Does the Heater Have to Be?

Heaters consume electricity, clearly, but how much exactly? Well, this depends entirely on the size of your fish tank. And different heaters are more powerful than others, being able to produce more or less heat. I personally use 5 watts per gallon of water volume, as I found this works best for my guppies. And just because I like you, here’s a handy list you may find informative:

  • 5 gallons/20 liters (tank size) – 25 W (heater wattage)
  • 10 gallons/40 liters – 50 W
  • 20 gallons/80 liters – 100 W
  • 25 gallons/95 liters – 125 W
  • 40 gallons/150 liters – 200 W
  • 50 gallons/ 190 liters – 250 W

Now you know exactly what wattage you want from your heater based on tank size. You’re welcome! I’d personally recommend the Eheim Jager aquarium heater since they’re quality-made and boast a handy thermostat.

What If You Keep the Guppies Indoors?

Understandably so, you’ll need a form of artificial heating if you keep the fish outdoors, especially if you don’t live in a tropical climate. But is it still the same if you keep the guppies indoors? Well, even considering you have a constant temperature of 70 °F in your home, water heats slower. I’ve personally tested this and found out that water will always be a couple of degrees colder than the environmental air.

So, if you have a temperature of 70 °F in your home, the aquarium water will only get up to 64-66 °F. And that’s not exactly ideal for guppies. In fact, it’s quite dangerous for them to live in such cold waters. To fix this, just buy a water heater based on the setups I outlined earlier, and you’ll be fine. Even during winter, the heater will keep the aquarium water just warm enough for your guppies to thrive.

What if You Live in A Tropical Climate?

That’s another thing altogether. If you live in a tropical climate with warm temperatures all year round, you can even keep the guppies in an outside pond. You want the outside temperature to never drop below 68 F (20 C). So, if you live in Hawaii, for instance, you won’t ever need a water heater since most times, outside temperatures never drop below 68 F.

There is a way to keep guppies in an outside tub even if you live in colder climates. Just set up the tub or the pond in early spring, when the temperature never drops below 64 °F. The tub or the pond will heat up substantially during the day, and during the night, it’ll maintain approximately the same temperature for a prolonged time. Water cools down slower than air, after all.

But be careful that you don’t overheat the tub or the pond. During hot summers, temperatures go wild, and your guppies aren’t fans of boiling water either. Just how they don’t like freezing water, lava-like water tends to put them off for good. So, I recommend planting a couple of trees or creating shade around the pool, so the water doesn’t overheat. Sunlight will still get to the water but not so much so it becomes too hot.

But when fall arrives and the outside temperatures start dropping, you’ll need to bring the fish back inside. You could try to maintain the temperature in the pond to a reasonable temperature but from personal experience, I can tell you it won’t work. It’s not efficient at all and you’ll only waste electricity. The fish may even become sick because the outside temperature is too cold, and the heater can’t compensate in due time.

What if The Water Becomes Too Cold?

What, will guppies just die if the water becomes too cold? No, not at first, if the water isn’t that cold. But you may start noticing your guppies becoming lethargic and sluggish. Cold-blooded animals like guppies will always mimic the outside temperature in their bodies. And having a cold body is both counterproductive and unhealthy, even for fish. They’ll become so stressed that they may even refuse to eat.

Then, guppies may even sink to the bottom of the tank if the water is cold for too long. That’s when other, more aggressive fish may attack them. With how weak their immune system is from not eating, guppies could become sick. Dropsy, fin rot, swim bladder disease, all these become more common and also more deadly.

Where Can You Place the Heater?

Clearly, placing the heater near the filter will be your best bet. As the filter circulates the water through the tank, it’ll heat it up evenly. This way, you won’t have a portion of the tank that’s much warmer or cooler than the other. If you have a bigger tank, I also recommend setting up multiple heaters. So, you can place one heater near the filter and another on the opposite side of the tank to more evenly spread the warmth.


I’d say that guppies need a heater to survive, indeed. Without one, they’ll become weaker and stressed. And by now, you should know exactly how dangerous stress is for guppies. It can even kill them, and I wish that was a joke.

A minimum temperature of 68 °F is required for guppies to live happily ever after. Any less than that and they’ll start becoming stressed and sick. With how feeble and vulnerable guppies are, they won’t last long in a state of weakness.

avatar Noah
I’m Noah, chief editor at VIVO Pets and the proud owner of a playful, energetic husky (Max). I’ve been a volunteer at Rex Animal Rescue for over 2 years. I love learning and writing about different animals that can be kept as pets. read more...

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