Interesting site. I have a few thoughts on their process:
The "mineralized" soil mix is essentially soil with natural mineral fertilizers put into it. Clay is a component of soil, as are silt, sand, and organic materials. If you go and dig in your back yard below the A horizon (often called topsoil), you will hit a clay layer. In some areas, e.g. the southeast, the clay layer is at the surface (topsoil has been eroded away). This is fine to use in the tank. No need to buy expensive pottery clay.
The main difference between that soil mix and what I like is that I increase the large organic matter in the soil whereas they remove it. As leaves and other organic debris break down, they release CO2 and can actually sequester nitrogen during the decomposition process. And it leaves behind material with a great CEC.
(Also of note - this type of "mineralized" soil, in which minerals are added, is different nitrogen mineralization - whereby organic nitrogen like protein is converted to inorganic forms like ammonium and nitrate.)
(Second also of note - algae discussion is very good; however, there are many other algae that cause green water, not just Euglena.)
I see the soil article as kind of a middle ground between the high tech/low tech people, if nothing else it's nice to see some high tech people doing something besides going out and buying the be all end all latest substrate from East Asia
Tis a nice basic algae overview.
NANFA Youtube Channel 
