Bettas are tropical fish that require warm water temperatures. Because they are often misleadingly marketed as bowl fish who require little care, many owners mistakenly put their fish in water that is too cold. Cold water poses a number of health risks.
Betta Water Temperature
Bettas need a water temperature between 76 and 80 degrees Fahrenheit. This is slightly above room temperature in most houses. In the wild, bettas live in warm rice paddies with low water circulation, high oxygen and stable, warm temperatures. You should reproduce these circumstances for your fish.
Cold Water Risks
Cold water can weaken your fish's immune system, exposing him to a variety of bacterial, fungal and parasitic pathogens. When water is not properly maintained, fish may develop popeye disease, a life-threatening condition that causes the eyes to bulge out of the head. Bettas stop eating in water that is too cold, and in very cold water they may not have access to enough oxygen. Your fish will quickly become lethargic in cold water and may hover near the bottom of the tank trying to get warm.
Heating the Water
The most effective way to heat your fish's water is to use a small water heater. Water should not be higher than 80 degrees, so ensure that the heater doesn't overheat the water; many water heaters are too large and produce too much heat for bettas because bettas are often kept in small two- to 10-gallon tanks. Check the specifications of the heater you've chosen, and make sure it is not intended for a tank larger than the one you have. Check the water temperature daily to ensure it remains consistent.