It seem that this thread, that I think really important, do not bring the interest I was expected.
First Soilmaster, Turface and other DIY stuff are really important for this hobby because they are inexpensive alternative to the stuff reserve to a certain elite that do not really want to take the time to understand what is involved in a good substrat, and buy the ready to use expensive stuff.
Good, now that this is said, Soilmaster and Turface are used mostly for their CEC (Cation Exchange Capacity) that is the capacity to retain nutrients in dissolution to make it easily available to the plants.
They are fired clay at around 1000F. At this temperature clay is vitrified it will remain in this state for thousand of years.
No more organic materials, no more soluble material. This mean that whatever the chemical composition, no leaching of any element will occurs or only a so small amount that it will not participate to any nutrient available for the plant. The real advantage is the CEC, or the capacity to grab nutrients, oxygen from the water and build a reserve available to the roots of plants.
Make your choice:
Soilmaster CEC: 19 and low PH 6 (remember that the lower layer will have tendency to lower this ph number and bacterial activity is not imperative to low ph)
Turface:CEC 29 to 41 and a higher ph of 6.2 that will be almost an ideal ph for the water column (achtung, we will need some kind off buffering capacity , like Soilmaster) to keep lower layer to have very low ph)