I recently purchased a used 5 gallon tank, an Ocean Treasures cylinder tank to be exact.
http://www.geekalerts.com/u/scuba-tank-aquarium.jpg

I set it up in my living room, but am having issues with it running fairly warm. Without a light or the lid on top of it, its at about 82-83 degrees. With both on, it runs closer to 86 degrees. I keep my A/C fairly low, 74-76 degrees, so I was looking for other options to help in cooling.

Here are my thoughts\ideas:
1. Changing the light to an LED.
2. Installing a fan
3. Setting up an extremely small custom wet/dry filter.
4. Installing a chiller of some sort.

Now, The LEDs are a cinch.. but aren't likely going to have that much of an effect on the temperature.
So, here are the main issues with the others...

The fan would be going in the dome shaped cover, which only has a tiny breather hole in the top of it. I'd prefer to not have to drill it, but I'm afraid that the covers (both the flat acrylic and the dome shaped decoration) will not allow for proper airflow.

A likely source of the excess heat, is the pump. It is a submersible Marineland duetto and I was thinking of removing it and trying another brand, or to make some sort of wet/dry filter either in the top compartment or the base (which each have about 3-4 inches of vertical clearance and a diameter of a little less than 14.5 inches). But, I don't even know where to begin.

And lastly, the chiller is just too expensive for an aquarium this small... and requires a bulkhead mount, which wont work for a cylinder, unless its either mounted in the top or bottom acrylic pieces, which brings me right back to the air circulation problem, since both are covered.

Has anybody had success in modifying theirs or a similar aquarium? Or have any other cooling ideas/solutions? Any helpful input would be appreciated. Thanks.