I have thought of trying Kanuma Hakone. It is expensive here! Have you tried Akadama?
What is kanuma? It looks like corn kernels.
Kanuma is a volcanic clay sub-soil. Quite acid and used in Japan for azaleas and indoor plants etc. It is mined from the side of a mountain. Akadama is red coloured and harder and sometimes fired. It comes from the same area but is higher in the soil profile. You can find them in various grades at your local bonsai supplier who imports from Japan. I think that's right Hakone?
Still in doubt if I'll let my acmondontum in this substrate. Popow reports good results and I don't mind testing this substrate with the plants I mentioned earlier but I'm not that keen on testing it with a plant I recently purchased.
The plants are not grown in that substrate, they are kept, it is a difference... If you get a mature acmodontum, and want to grow a couple of leaves, keep it nice until it's sold, akadama or kanuma will do it. If you want to get a complete root system, and grow on the long term, then it is not suitable...
I'm from Japan, so I'm somewhat familiar with those media. Kanuma is pretty specialized soil. Unlike Akadama (which is mildly acidic), Kanuma is highly acidic, so they are used for acid loving plants like Azalea and bonsai of rhododendron (Satsuki). For some Japanese/chinese temperate zone Cymbidium, Kanuma is used. So it is interesting to see how paphs would do in highly acidic media. Akadama can be used for more general plants (e.g. some people use it for orchids). Both of them retain water well.
I guess I have finished testing of different substrates for paphis and stay with my simple mix . Though, interesting to read progress in this new substrate.