Evaporation depends on ambient humidity. The lower the humidity the more evap and more cooling. I maintain a 20 liter tank but humidity is around 80% here in Japan so with 4 4-inch computer fans I still had difficulty keeping water temp below room temp. To solve this I got an old beer cooler, filled it with ice packs and saltwater, plumbed an overflow into it and placed it above my tank. My tank had a thermostat controlled pump that pumped water into the cooler which caused the chilled saltwater to overflow back into the tank. It was a poor man's chiller and required replacement of the ice packs every 4 or 5 hours but it saved my acros last summer.
