Hi there TommyR, the potting mix is Primeagra or Hydroton which is used for semi-hydrophonic planting. I got my first Primeagra from First Ray's Orchids and the rest is Hydroton which I got a BIGGS Wherehouse they sell everything for Hydrophonic gardening. (The medium is special clay granules for Hydroculture. The shape and international structure of the pepples ensures good root areation and prevents rotting, excess acidity and soil pests. The pepples have astable structure and outstanding capillary properties. ) This was taken from the bag of Hydroton.
Hope this answers your question
TTFN - Sheridan