I used to used thos 12 volt aux fan for computers. I have the 4 or 5 inches version... not sure.... but sure bigger than the regular ones.
Then I heard these 7 dollar fans from Wallmart. The problem was it is quiet big and heavy so I was forced to put it on sump. Did not help at all. my temp went to 86. WOW. I even add one full size stand fan blowing on the sump but still, no can do.
I went back to my old config. Just one 12 volt aux fan positioned between the tank and the canopy. It kept my tank to 80. Amazing. So like curtswearing said... air to the surface of the water specially to your main tank, makes a big difference.
Hmmmm.....Reedmans idea is very interesting. I have a friend in Manila that uses those water dispensers that has HOT and COLD thing where you put your 5 gallon containers.... the same idea.... very long hose coiled to the condenser I think. Just make sure that you use the cold side and not the hot side (evaporator).... and considering the temp in the Philippines, it works for him.