Our water is V hard, so I could imagine that (eg) the clay particles could become ionically saturated with some component of calcium carbonate, reducing it's capacity for more useful nutrient storage.
(Obviously I'm not a chemist, so this may make no sense whatsoever! )
Hi Marcel,And volcanic substrates have the worst CEC of all CEC substrates but seem to grow crops like a champ.
There are different types of volcanos and therefore different kinds of volcanic rock. The "worst" volcanic type your article might have been referring to would be perhaps be some types of pumice, but the material formed by lava has a fair to middling CEC. The worst material as far as CEC goes is sand.
Hi Marcel,Hi Ceg,
The PC these bookmarks are on is dead, I would need to take out its HDD to see if I can recover this bookmark. And I saved it quite some time ago somewhere around 2015 when I first used Akadama and that CEC thing about it got me curious, so I started reading about it and found this article. I actually do not know if this is still online, could be long gone after these years. I give it a go and if it's still there I'll post it. The article had nothing to do with the aquarium it was all about vulcanic soils in general from different regions and also their CEC tested and all came back with a rather low number.
The bottom line conclusion I could make up from it was that a good CEC might be helpful but isn't a necessity to farm crops as long as all nutrients it needs are available.
Then personally seeing a 1500 litre aquarium bursting with lush growing plants growing on plain sand only pushed me over the line not to worry about it anymore. And when buying aquarium soil that the Good CEC on the bag's label is something rather neglectable when it comes to growing aquatic plants.
I also wouldn't know how to test it and or interpret and determine the results in what is what.