I think you have the answer not enough air . I would not put it in the outside pot , if you have a sodering iron add larger holes to the bottom of the plastic pot .
It has been wet here too , on the wet gloomy days I don't water anything not even the mounted or Vandas . If you have some Physan it would work to get rid of the mold . Or 2 cups regular Peroxcide to a Gal. of water poured thru the pot it will also get rid of the pesty fungus knats . Gin