Many betta owners are not aware that their betta requires warm water, not just the room temperature water that ranges from 68–72 degrees Fahrenheit (21–23 degrees Celcius). Ideally, the water should be between 78–80 degrees Fahrenheit (25.5–26.5 degrees Celcius) for a betta. Because bettas are often kept in very small tanks or bowls, heating can be a challenge. Changes in room temperature, especially in buildings or climates that become much colder at night, can prove stressful for a betta. However, there are several small heaters made specifically for mini aquariums and betta bowls.
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.
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 tanks or bowls.
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.
With the advent of very small heaters, manufacturers are moving beyond the standard torpedo style heater that is suction cupped to the side 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 bowl or tank itself.
Regardless of the type, size, or shape of the heater, they do not come with built-in thermometers; there is no way of knowing what the temperature actually is. Therefore it's important to use a thermometer to check your water temperature regularly. 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.
Bettas Need More Than Bowls. University of Illinois at Urbana-Champaign College of Veterinary Medicine, 2020