i have 4 20 gallon fish tanks in one room on the third floor of a brick apartment building in Chicago with little air conditioning. I tested one fan to see how much I could drop the temperature on one tank. I removed the glass cover and light and ran the fan overnight which dropped the temperature from 84 to 78. The noise of the fan is minimal. The only trouble I have with this fan is adjusting the plastic clamp on the arm to secure the fan to the tank. The clamp is difficult to slide and I am afraid of breaking off this plastic clamp.
My 55 gallon goldfish tank was running too hot. After staring at chillers, and fans, I decided to try this out. Much to my delight it has lowered the tank temperature from 84 to 74 degrees. Sometimes even lower depending on ambient temperature. It does make some noise, like any fan, but nothing objectionable.