I have tried Akadama nd Kanuma both, and although they do break down athey take at least 2 years to do so so ne fear in using them.Jamie wrote: if you can get diatomite, actual diatomite i recommend it over the others. cant say on akadama or kanuma either, havent used it, but dont think i will be interested if it collapses and gets gluggy.
My thoughts are they the Japanese use these soils because that is what they have locally available and only in the last 50 years( or less) have foreign materials become available. They have been growing trees in it for 100's of years and are happy to continue doing so.
If they had Diatomite in Japan thne I am sure they woud be using it as well, and possibly even in preference to Akadama.
I have tried Our local D, and both Akadama and Kanuma, and will not bother with akadama any more as it is not worth it when I beieve a Better medium available locally and cheaper

Kanuma I am still keen on only as the Azaleas in it are doing extremely well. I have yet to Confirm the performance of Azaleas in Diatomite is the same or better. I have Azalea Cuttings in Diatomite doing real well so they look promising. I will know in 2 years and that is when all my Azaleas will need potting again
Ken