seems like fungus growth to me. Mold, mildew, fungus, dont really matter though because all originate the same way, high humidity and/or constant dampness. My opinion is repot that whatever you have growing in there. Then buy a hygrometer to check your humidity, and watch how much you water, only water again when the top couple inches of yer pot is so dry its nearly crusty. By that point theres only a tad bit of moisture left in the pot. If your one of those "you wanna make what you have work" kind of people and you dont wanna buy anything, only thing i can say is put your plant in front your central ac vents, and turn the heat on to dehumidify the hell out of it, and dont water it for a good week. If it starts to appear thirsty foliage feed it by misting it. Good luck.
Edit: Or buy a dehumidifier obviously but that seems like alot of fungus, imo it would take longer to get rid of the fungus then to replant it and just deal with the few days of no growth.