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What Is the Best Water Temperature for Betta Fish?

betta fish in bowl
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The ideal betta fish water temperature is between 76 to 81 degrees Fahrenheit. These tropical fish require warm water, and room-temperature water is often too cold. Changes in room temperature, especially in buildings in cool climates that become much colder at night, can prove stressful for a betta. Here's how to establish and maintain the proper water temperature for your betta fish.

Betta Fish Water Temperature Control

A betta fish needs water temperatures to remain between 76 to 81 degrees Fahrenheit, or 25 to 27 degrees Celsius. Room-temperature water ranges from 68 to 72 degrees Fahrenheit (21 to 23 degrees Celsius), which is too cold for these tropical fish. Bettas are often kept in small aquariums, so heating the water can be a challenge. However, there are several small heaters made specifically for mini aquariums, each with pros and cons.

Fully vs. Partially Submersible Heaters

The term submersible refers to a heater that can be fully submerged in water. However, some manufacturers use the term “partially submersible,” meaning that a portion of the heater must remain above the waterline. Generally, partially submersible heaters cost a bit less but are not as versatile. It is recommended to use fully submersible heaters whenever possible, no matter what the tank size, as they do a better job at creating evenly heated water. Submersible heaters are also less likely to get damaged by water or cause an electric shock in the tank.

Pre-set vs. Adjustable Heaters

Pre-set heaters come with a single preset temperature, generally 78 degrees Fahrenheit. There is no way to adjust preset heaters; they simply turn on and off as needed to reach the factory settings. However, these are often smaller and less expensive, which makes them a good candidate for small aquariums.

Adjustable heaters come in two varieties. One has temperature markings that allow a specific number to be selected. The second type has an adjustment knob labeled with only a plus and minus; these heaters have a small light that comes on when the heater is putting out heat, and you choose the setpoint. To adjust the setpoint, you must first place a thermometer in the tank. Next, turn the heater on and wait for the temperature to reach the desired level on your thermometer. Finally, turn the knob until the light goes out; this new setpoint temperature will then be maintained.

Heater Shapes

With the advent of very small heaters, manufacturers are moving beyond the standard torpedo-style heater that is suction cupped to the inside of the tank. Heaters now come in a variety of shapes and sizes. Some are flat, while others are rectangular-shaped. Betta heaters are rounded to fit in the bottom of a bowl.

One thing they all have in common is that they are made from shatterproof materials and require little energy to run. Flat styles can be placed under the gravel, thus avoiding the need to try to hide the heater behind decorations. It is even possible to place some flat heaters underneath the aquarium itself, attached to the glass on the bottom of the tank.

Thermometers

Regardless of the type, size, or shape of the heater, it won't come with a built-in thermometer. Therefore, it's important to use an aquarium thermometer to check the water temperature regularly and ensure that the heater is not underheating or overheating the water for your betta. Small stick-on, color-change thermometers are ideal for mini aquariums and are quite inexpensive.

If the tank is very small and a stick-on thermometer would be visually unappealing, a standing thermometer can be placed in the tank for a short time to take a temperature and then be removed.

Why Does Betta Water Temperature Matter?

Water temperature significantly influences fish behavior, metabolism, growth, and immune system function. In the wild, bettas live in warm parts of Southeast Asia where the water temperature is always warm. They have not adapted to live in cool water temperatures. If the water temperature is too low, your betta fish may become lethargic and sleep more than usual due to a slowed metabolism. If the water is too warm, the fish may swim erratically and struggle to breathe. Maintaining the appropriate water temperature for your betta fish can help them live a longer, happier life.

How to Safely Adjust Water Temperature

Water temperatures that are too cool or too warm can affect your betta's health, but sudden temperature changes can be stressful to fish as well. It's important to gradually adjust the water temperature if it's not at the optimum level. Also, be mindful during water changes, which can cause significant temperature fluctuations. Always adjust the new water to the proper tank water temperature before adding it to the aquarium when doing partial water changes or topping off the aquarium.

If your betta fish shows signs of illness or you have questions about maintaining your betta's habitat, contact a fish veterinarian for advice.

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  1. Bettas Need More Than Bowls. University of Illinois at Urbana-Champaign College of Veterinary Medicine, 2020