I am not sure what you mean when you say bark nuggets....
Miltoniopsis do well in a water retaining mixture. Small orchid bark mix, rock wool mix and New Zealand sphagnum moss mediums work well. It is important that the pot has adequate drainage. These plants like to be somewhat pot-bound so allow room for only one year's growth. Repot once per each year, preferably in the spring. hope this helps and if you need to repot your Mitonia this would just be a good time to do so if it is not in flower. [color:"blue"] [/color]