Hi Luke
Personally I would not be worried too much about the PH of a inorganic mix at all.
Supposedly, Mt Sylvia has a PH of 8 or more, and Grant initial tests agreed with, but his subsequent tests it turned out neutral.
I have Azaleas Happily growing in Mt sylvia D, and if it was really a PH of 8 then they would cark it in no time. Over about 4 years of use, I have proven that they have no problem at all, and in fact perform and well as those in Ray Nescis Commercial Bonsai potting mix.
I can only assume, that this is because The PH is in the dust particles only and they wash off in days, or the high PH leaches out in very short time, or is counteracted by Zeolite. Whatever the reason, for my own use and from my own experience the Supposed high PH is irrelevant.
I started out looking for components to make Boons mix here in OZ, and the only thing I could find was akadama and that was stupidly expensive and was put onto Diatomite by a Bloke in the U.K. Turface I could never source here, but I believe is available in NZ.
I tried diatomite, and have never had a reason to use anything else as it has all the properties that I require, and its growth performance is as good or better than anything else.
The only thins i will try now is adding some Pumice as we now have a source for it in sydney.
See my Test thread here and another year has passed and I still see the same results.
viewtopic.php?f=12&t=2056&p=85469&hilit ... ite#p85469
Ken