I recently replanted a starter ficus from basic potting soil to somewhat course bonsai soil. Right near the base of the trunk it was hard to remove all of the potting soil without damaging the roots. So I left a little of it, it was about a month after the repotting that a white fuzz like substance began appearing. It's been about two weeks and when I water it I run the water lightly over the substance and it goes away for a day then comes back. The plant is not dropping leaves and new shoots are still forming. I have been careful not to over water the plant but I think the little amount of potting soil is just holding too much water and not drying up as fast as the bonsai soil. If this is the case should I repot again and make sure to remove all of it? If too soon to repot again, Is there any recomendation for something to spray it with?

Thank you

Eric