Soil (CEC= 24+) has a CEC almost as high as any of the Montmorillonite clay substrates (CEC= 27) such as Soilmaster Select, Turface, and STS. Sand has a CEC of basically "0" and Flourite has a CEC of about 1.7. As I understand it, it is the high CEC that causes a substrate (or soil) to absorb minerals and nutrients and make them available to the plants in the root zone.
Lots of our members like the ADA Aquasoil products like Amazonia which has a high CEC. What are aquasoils?
aquasoils are not gravels. They are made by mixing nutrient rich tropical soils with colloidal clays (totally “dissolving” in water) as bentonite/montmorillonite/fuller’s earth/palygorskite or akadama like clay, or volcanic ash soil, than dried at moderate temperatures, i.e. they are NOT “fire kilned”. Clay surves as a binding agent, but the main thing such clay gives to substrate is a high CEC - ability to hold nutrients and releasing them only when plants needs them. Tropical soils is a source of nutrients stored in organic form. They also have very high humic substances content which enables aquasoils to lower pH and GH for a big time frame creating mild acidic environments for keeping water plants and shrimps. Organics and humics also creates perfect environment for bacteria and protozoa greatly facilitating cycling all natural processes of a tank. Tropical soils and humates have very high CEC also.