this was a direct question to amano with his reply......
Q.1)  What are the major differences in the characteristics of Aqua Soil Amazonia, Malaya, and Africana? What are they specifically in terms of the ability to decrease pH, the effect on KH, and the brittleness of soil particles?
A.1)  The differences among the Aqua Soil Series substrate materials are primarily the amount of nitrogen (organic materials) and pH decreasing (same as kH decreasing) effect as described below:
Nitrogen content in descending order:
Amazonia -> Amazonia II -> Africana -> Malaya (contains practically no nitrogen.)
* Aquatic plants grow better in a substrate with higher nitrogen content. Thus, they grow better in Amazonia and Amazonia II.
Ability to decrease pH in descending order:
Malaya -> Africana -> Amazonia II -> Amazonia
* As pH decreases, KH also decreases. Malaya and Africana are best suited for the purpose of decreasing pH.
As for the brittleness of soil particles, Malaya has particles that are the most brittle and easiest to break up. The brittleness is about the same among the other three types.