This came up in another post of mine regarding a bad heater but I've had amazing success with a simply fan. The first day I tried it, I aimed the thing at the top of the aquarium and in a room that was 85 degrees, I got the water in the tank, which was at 80, to go down to 75. Granted, it took a gallon of water to do it, but that's small potatoes in my book if it means a simple fan can keep my aquarium cool without a chiller.
Consequently, I also raise chickens here on my little homestead and I freeze 2 liter bottles every day and give one to them-- immediately begins to melt and give them cool water during the warmest period of the day. I imagine the same thing would work well for the aquarium.
BTW, I have the fan on a timer-- turns on with the first bank of lights. Had to readjust it because it was TOO effective.