Water and bettas are like air to humans. You should change your water by about 20-25% a week as a preventative measure to ensure that your tank is clean. When you change water, make sure that the temperature of the new water is roughly the same as the one in the water tank to avoid harming the fish. If you have a filtration system in your tank and you change the water twice a week, you are already conducting a Nitrogen cycle. The cycling process can take a month to complete successfully and you will notice the nitrates and ammonia levels fluctuating before being balanced out by bacteria to zero levels of ammonia and nitrater at 5 -10ppm.
