Chemical and mineral build-up is a common problem for Dracaena and has everything to do with your water. To try and correct the problem I would try adding some new soil to the pot that does not have added fertilizer and begin watering with water from a different source than what you have been using. Fluoride is added to tap water in some areas, so if you have been using tap water for this plant you may want to use an alternate source of water. Filtered water can work from a standard water filter can also work. More complex types of filtering systems can cause other problems.