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Why It's Important to Keep Temperatures in an Aquarium 

fish tank

Have you ever wondered why some fish owners have a thermometer in their fish tanks? Aquariums are miniaturized ecosystems, and they require a careful and specific combination of factors for them to sustain life. One of these factors includes temperature.  

In rivers, lakes, and other bodies of water, the temperature can have a significant effect on how fish grow, reproduce, and feed. This is why you can't find certain fish in rivers during winter or summer. When the water in your aquarium changes temperature, your fish may succumb to the changing temperature's harmful effects.  

Along with the adverse outcomes of changing temperatures, here are some of the reasons why it's important to keep your aquarium temperatures at the right level: 

  1. Sudden changes can kill your fish! 

As you know, fishes are poikilothermic, or cold-blooded animals, meaning their body temperature will depend on their surroundings. In this case, it's water. If there's a sudden drop or rise in the water's temperature, the poor fish might go into shock. Worst case scenario is that the fish could die. With this in mind, water temperature isn't just important—it's vital.  

To keep your aquarium at a stable temperature at all times, you'll need a trusty water thermometer. It's easy to find one online, we recommend or you can go into your local pet store to get one. Make sure to read reviews before deciding on which brand to get.  

  1. Fish can suffocate in warm water 

It sounds silly to say that your fish can ‘drown,’ but they certainly can, especially in warm water. There's a perfectly sound explanation to this—there's less oxygen in warm water.  

Fishes, just like other living creatures, need oxygen. As temperatures rise in your tank, oxygen levels decrease. And sure enough, the likelihood of your fish suffocating, or ‘drowning,’ also increases.  

Being aware of how warm the water is matters—the tank shouldn't exceed 90°F/32°C. 

  1. Tropical fish won't survive in cold water 

Next up is colder temperatures. Some fishes might be okay in chilly water, but tropical fish are different. If you have tropical fish, keep the water temperature at around 75–80°F/24–27°C. That being said, tropical fish shouldn't be mixed in the same tank as fish that thrive in cooler waters (60–75°F/15–24°C). 

Important reminder! 

The recommended water temperature depends on what kinds of fish you have:

  • Tropical fish: 75–80°F/24–27°C 

  • Cool water fish: 60–75°F/15–24°C 

Location is key 

Before anything else, it's crucial to get the placing of your aquarium just right. If it's always dropping or rising, then the spot you have it now might not be an ideal location. For instance, a place that gets hit directly by sunlight would experience rapidly fluctuating temperatures. 

How to increase or decrease the aquarium's temperature? 

Depending on where you live and the local climate, you'll probably need to heat or cool the water temperature. You can do this with the following devices:  

  • Pre-wired temperature controller 

The best option for controlling your aquarium's temperature is to get a device called a pre-wired temperature controller. It does all the work for you—all you need to do is to install it. But if you think that this device isn't for you, there are other options for tank owners.  

  • Aquarium heater 

If you notice that the water temperature is dropping, you'll need to heat the water. To do this, you'll need an aquarium heater. The great thing about an aquarium heater is that it will automatically stop heating at the set temperature.  

  • Devices for cooling 

To cool the water, you could opt for a fan or an aquarium chiller. The latter is typically used for larger aquariums.  

You can also try to keep the room cool with your AC, but it might not be possible at all times, so getting the right devices would be the better choice.  


Again, to make sure you have all the information you need—fish can die from sudden temperature changes, and also if it's too hot. Tropical fishes can't live in cooler temperatures and shouldn't be mixed in the same tank with cool water fishes. 

Now that you know just how critical it is for the fishes to keep the temperature at the right temperature, you probably understand why so many fish owners use all kinds of devices. Aquariums are unnatural habitats for fishes, and keeping this small ecosystem thriving requires all the help it can get. So, please, for the sake of your pets, use a thermometer.