The ideal temperature range for a betta fish tank is between 78-80°F (25.5-26.5°C) . Although betta fish can tolerate temperatures ranging between 72-86°F (22-30°C), if the water is outside of their ideal range, they may not thrive and can become susceptible to diseases. To maintain the ideal temperature range, it is recommended to use a fish tank heater and a thermometer to measure the water temperature and make sure it doesn’t go above or dip below the ideal range. If the tank’s temperature is not right for your betta fish, it can cause physiological changes in your fish that lead to odd behaviors. It is important to note that colder water can kill the betta, as the bettas immune system will slow and make them susceptible to disease, while hotter water can make them uncomfortable and age quickly, as their metabolism will increase.