Doc, the stuff I use is "Shultz's soil conditioner" AKA Turface, which is the name most know it by. They are the exact same product both made by Profile LLC. The difference is that Turface is mainly sold to large grounds keeping outfits like for golf coarses, football fields, etc. It is particles of clay that have been fired in a kiln at high temps so what you end up with is like small ceramic particles, most between 1/8 to 1/4". It has tiny pores on the surface which hold moisture that I think helps with fine root development. It's a good component for bonsai soil, give it a try if you can find it.

I'm also trying a mix with crushed brick that looks promising but I haven't used it long enough to recommend it to anyone. I would like to try crushed lava but the smallest I can find is around 1 inch and I seem to have lost my sledge hammer LOL.

Tony