I have a 75 gallon aquarium and I was wondering, how do I keep it cool? I haven't been using a heater in my tank for this summer because its upwards to 100 degrees outside. Its pretty hot in my room because I was shutting my door all the time and not letting air circulate so it got really hot. Especially since I have a beast computer with 3 monitors running a lot. So back on the question. How do I keep my tank cool? At the moment, the tank stays at about 81 degrees -which all the fish in my tank can handle really- but I wanted to cool it down so it would be the best for my fish. I've tried ice in a bag but I feel as if I tried a full bag of ice, the temp. will fluctuate too much and will stress my fish. I just want to cool it down a couple degrees