NO! Not ice! It will freeze the little guy. What I do is take a bucket of dechlorinated water and fill the basement sink with hot water. Then I put the bucket of d. water in the hot water (not mixing the two waters) until the temperature reaches 75ish. Usually for about 10 minutes. Then take out some of your bettas 83 degree water and add the cooler, dechlorinated water. Also, make sure your betta is not in direct sunlight, this is what might be causeing your temperature to get that high. I keep mine between 78-80*F, although for medicating your fish its okay to have it at 82-85*F.