For the vinegar suggestion, I didn't intend that vinegar be applied to the leaves of the plant - which would be harmful especially out in the hot sun.! Only that after scraping off the mold (or whatever it is?) give the root ball a soaking in a very dilute vinegar/water bath before re-potting and topping with fresh soil.
Since we don't have a photo of the plant or the stuff growing on the soil, and since the OP has not checked back in to read/comment, I figure we could all just keep throwing out various ideas hoping that one will hit the mark. Seems to me each of the ideas have some merit.
