Guppies are tropical fish and they like warmer water. Although guppies can survive in lower-temperature water, the chances of developing some types of disease are really high.
So, do I need a heater for my guppy fish tank? The short answer is, YES! You need to heat the water for your guppies, unless you live in a tropical climate, where the temperature does not drop under 68 °F (20 °C).
Guppy Aquarium Heater Size Guide
If want to calculate the wattage you need, just use the basic rule of thumb: 5 watts per gallon of water volume. The following table is for in-door aquariums, where the room air temperature is set to 70 °F (21 °C).
| Tank Size | Heater Wattage |
| 5 Gallon / 20 Liter | 25 W |
| 10 Gallon / 40 Liter | 50 W |
| 20 Gallon / 80 Liter | 100 W |
| 25 Gallon / 95 Liter | 125 W |
| 40 Gallon / 150 Liter | 200 W |
| 50 Gallon / 190 Liter | 250 W |
| 65 Gallon / 250 Liter | 2 X 200 W |
| 75 Gallon / 285 Liter | 2 x 300 W |
With this setup, you will be able to heat up the aquarium water to up to 80 °F (27 °C).
I use and recommend the Eheim Jager aquarium heater (on Amazon.com), which has a thermostat. These heaters are ver reliable. I use multiple of them and have never failed me. I have one, which I use for more than 8 years and still works perfectly.
Keeping Guppies In-Door
Do you need a heater if you keep your aquarium in your home which is heated?
If you live in a climate, where you need to heat your home in the winter, probably you will set a temperature of 70 °F (21 °C).
Guppies can survive in a water temperature of 70 °F. The only problem is that your aquarium’s water will not have the same temperature as the air. The water heats up slower than air, and also cools at a slower speed.
I’ve observed that in a room, where the air temperature is set to 70 °F, the water will heat up to only 64-66 °F (18-19 °C). This is dangerous for your guppy fish.
If you are rolling with these parameters in the winter, you need to get a heater for your guppies. I use the Eheim Jager 50W aquarium heater. This is great for keeping a constant water temperature of 74 °F (23-24 °C) in my 10-gallon guppy aquarium.
Keeping Guppies in Pond or Tub
If you live in a tropical climate, where the temperature in the winter do not drop under 68 °F (20 °C), you can keep guppies outside in a pond or tub.
In the following video, this person shows his guppies, which are kept outside in tubs. He lives in Hawaii, where he keeps guppies outside all year round.
He does not use a heater for the tubs, because the average temperature in Hawaii does not drop under 68 °F (20 °C).
You can still breed and raise guppies outside in tubs or ponds, even If you live in an area where the temperature drops under freezing level. The key is to setup your tubs or pond in the early spring, when the temperature does not drop under 64 °F (18 °C).
During the day the sun will heat up the water in the pond well enough to be safe for your guppy fish. During the night, the water temperature will not drop so significantly, because water cools down slower than air.
During the hot summer, you might want to create some shade around the pond to avoid overheating the water.
Once the temperature starts dropping in the fall, you should consider moving your guppies inside. To a certain extend you can use heaters to keep the water temperature of the pond at the desired level, but it is very inefficient in my experience.
I live in Continental climate, wherein the winter the temperature often drops under freezing level. Though I’m still able to keep guppies outside in my yard for 6-7 months without using a heater.
In the winter all my tanks are heated with one or more aquarium heaters.
Conclusion
Hopefully, this article has helped you decide whether you need a heater for your guppy fish or not. If you have any questions or want to add something to this article, feel free to comment below.
I read and answer all the comments on this website.
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Featured Image: https://www.flickr.com/photos/nathaninsandiego/5368202613/