try this ... http://www.shopjebo.com/63/aquarium_coo ... etail.aspx. (got it in SLS at a very good price)
But mine is double the size (4 fans all together). As what Steven said, it very much depends on the room temperature and also the size of the tank vs fan size. I overcrowded my tank with this 4 pieces fan and it took up almost 40% of my tank place.
But i can steadily said it will lower down the temp to 3 degree. I'm assuming that because with the lighting on (55w), the tank temp will reach 25 degrees compare to the normal 28 degrees. I wonder if i on it 24 hours ... will it get to 24degrees. Have yet to try, but will do it over the weekend.

