How to prevent mold and mildew around a aquarium?

I have a 29 gallon aquarium and would like to move it inside but have had problems in the past with mold and mildew on the wall next to the aquarium. I cannot afford a dehumidifier, and this would actually replace our humidifier. I want to prevent the mold from happening in the first place, i already know how to get rid of it.
Not algae, MOLD, not on the aquarium on the WALL!