im having the same problem but my fish arent dieing i have a clown gobie thats doing just fine. my temp hangs aroun 80 with the lights off and 83 with them on.
i found a place that sells chillers pretty cheap but i havent bought from them yet http://www.aquatictech.com/chillers.html
they are the cheapest i can find
the aquarium temp ussualy is higher than room temp because you have the heat put out by the pumps and lights. if you have a closed hood like the jbj nanocubes or the current aquapods try duct taping the little lid open that is used for feeding that should lower it a degree or two
(duct tape fixs all)