Last year, my tank was hitting temperatures that were a little high for my scrimps. I wound up losing a bunch of them. I was throwing ice ubes into the tank in the morning when I was leaving for work. Finally, I bought a fan and proppped the glass lid open and blew the fand across the water surface like vnghost suggested. This actually dropped the water temperature by a couple of degrees and did the trick! Only set back to that one is that it helps to speed up the evaporation from the tank. Just gonna have to keep topping it off if this is the route you decide to go! I hope that this helps!