Passive cooling of an aquarium using fans is a popular method for temperature control.

For evaporative cooling to work efficienly it relies on a steady flow of dry air from the atmosphere around the aquarium to be moved over the water's surface. This will allow for increased evaporation and as a result cause a cooling effect. There does not need to be any force to the stream of air for this to happen and a gentle even flow is best. If the air movement at the surface of the aquarium is strong, especially on a saltwater aquarium, small droplets of water can be blown from the surface causing excess salt creep around the edges of the aquarium or in extreme cases surrounding surfaces.