What kind of lights are you using? If you use 2 fans, it will create twice the noise. You may be able to use 1 fan, if you put a hole on the other end for air intake.. ! in, and 1 out, may not be as efficient as you think. The same cfm is tranferred (cubic feet per minute) since you can only exhaust as much as the 1 exhaust fan can handle. Input fan doesn't matter, any excess will be blown down at the water, heating it.
If anything, and you need 2 fans, set both for exhaust, and let the make-up air com from over the tank. However, you may have more evaporation, and you'll need to keep up with the replenishment of fresh water.