Bettas are a tropical fish that have several specialized environmental requirements, but temperature may be the most important. Your cold-blooded betta can quickly die if he's exposed to water that is too cold or too warm, or a sudden change from his normal environment, which is preferably a balmy temperature.
Bettas require at least one quart of water per fish, rather than the tiny bowl that many are sent home in from stores. The larger the tank, the more work -- or equipment -- required to heat it. Regardless of the tank's size, however, each can be tricky to keep at the proper temperature depending on where it's located in the house, the amount of water it holds, and how much water you need to change weekly to keep the betta healthy. All tanks should have an aquarium thermometer taped to the inside to keep close track of the water's temperature daily.
Bettas in small tanks with no filtration can thrive in water that reaches room temperature when the surrounding air is consistently 75 to 82 degrees. Simply place the tank in a small, sunny room -- but not in direct sunlight -- that can be closed off to keep it warm in the winter, or opened in warmer months to keep it from overheating. Larger tanks with filters keep the water cooler than the surrounding air and will require additional heating assistance.
For smaller tanks in cooler rooms, a heating pad developed for gardening seed trays or reptile aquariums may be the answer. While these do not have a controllable thermostat, you can monitor the water temperature by the thermometer; simply unplug the mat in summer months when the water remains warmer from the room temperature. For larger tanks, you can attach a heater with a thermostat that hangs in the water to the side of the aquarium.
Smaller, unfiltered tanks -- one gallon or smaller -- need a complete water change one to two times a week to keep the betta healthy. Leave the water out overnight to make it room temperature, or heat it on a garden seed or reptile aquarium mat to keep it at the same temperature. Larger tanks controlled with a heater need a 20 to 50 percent water change once a week. This will require heating the fresh water with a heater, as well, to avoid shocking the betta.
- fish in bowl image by Robert Calvillo from Fotolia.com