We recommend removing any visible mold and decreasing watering for the plant with mold present because mold is almost always a direct result of over-watering & poor ventilation. In addition to watering less, try moving your plants to an area with more air flow which will make it difficult for mold spores grow in your soil. It's also very important to add a natural anti fungal (like cinnamon) to the soil to prevent the mold from coming back.
Here's a quick guide on mold & houseplants with helpful tips:
http://www.wikihow.com/Get-Rid-of-Mold-on-Houseplants
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