You can do the water bottles, or if you already have ice cubes available, put them in a baggie and put them in the tank. There are water chillers available, but they are large, expensive, and obnoxious. Might be something to look at though. There are fans that have built in air conditioners you can get at Walmart for around $50-$60 to keep that particular room cooler.
I know that it's your tank room, but if you aren't able to find a way to cool down the fishes, it is probably best for their sakes to move them elsewhere in the house, at least for the time being.