Pumice.
Pumice has a slightly acid PH with a great water holding capacity of around 60% and it is a hard medium so it will not disintegrate after handling or re-use so it is great value if you recycle your mixes. Pumice is great for Azalea because of its PH value and its ability to open up a potting medium.
Expanded clay.
This expanded clay has a PH of around 6-6.5 and has a water holding capacity of around 40%. It is also a hard medium like the Pumice making it great value. There is a comment from the author of Pine Bonsai In The Temperate Climate regarding the use of this product with Pine Bonsai.
I am able to supply them so feel free to send me a PM if these are of interest
