Small fan helps a bunch, also just wipe it off if it's not appealing to you, or turn it into the soil. It probably wont harm your plants, a fan will help strengthen your plants and give small bugs a harder time to stick around like the fungus gnats I was battling. You may not be over watering as much as inadequate drainage/ventilation. I found bottom watering to be the best as Patrick suggested to me before, it kept the surface of the soil neat instead of pouring it on from the top.