Why dose anything if it's going to remove all the nutrients? It's as though they are saying that you should have a nutrient rich substrate but nutrient poor water. This seems to go against everything that I've been reading (and seeing in peoples tanks).
It has a high cation exchange capacity (CEC), like many other good substrates out there.
The plants can still use water column nutrients too, especially if dosing daily like many of us do. But substrates with high CEC can also remove some nutrients from the water and store them. The plants can then use them via their roots, that is generally a good thing - like spoiling the plants through feeding their leaves and roots.
Tropica also state that their substrate has no impact on pH or hardness, so the CEC can't be "too high", otherwise we'd see a pH and hardness crash, like with ADA Aqua Soil.
Hopefully JamesC, our resident chemist, will chime in.
Surely it would be better to use a totally inert substrate and add whatever fertilisation you feel is necessary whether it be through the water column or in the substrate as well. At least then you are adding what you see fit, since I imagine that you couldn't measure/quantify what the Tropica substrate has gathered (for want of a better word). Just a thought!
Not quite sure why they've said this. Most likely because it sounds good to people who are just starting out and also they are trying to sell a product so need to try and hype it up a bit. It's supposed to be very good though.
I've noticed that high CEC substrates do seem to grow plants better even though they are usually fairly inert. The one problem with high CEC substrates is that initially they do soak up a lot from the water, but this does settle down with time. These substrates work an exchange mechanism where they exchange cations in the water for hydrogen ions. A cation is a positively charged ion such as Mg++, Ca++, K+, NH4+, etc. This is why when you use ADA AS or any other CEC substrate you will notice the GH drops. Also as hydrogen ions are released you will see a decrease in pH and KH. Sound familiar? The KH drop is not, as some believe, the substrate absorbing HCO3, CO3.
So what's better, a zero CEC inert substrate or a high CEC substrate? IMO a high CEC gives me better results. The one down side to high CEC substrates is that they require lots of water changes when first used until they settle down.
Tropica substrate by comparison is buried below another substrate so the effect of exchange of cations from the water will be reduced. I have read somewhere that actually Tropica and ADA substrates don't actually contain a great amount of nutrients, but don't quote me on that. Tropica add Sphagnum moss to theirs which provides nutrients and ADA provide Power Sand which also provides nutrients.
There are 2 forms of ammonia. Free ammonia - NH3 and ionised ammonia - NH4+. They are in equilibrium in water and this equilibrium is determined by the pH of the water. So the only ammonia we are concerned with here is ionised ammonia. Zeolite has a massive CEC value and this is the reason why it is sometimes added to new setups to reduce ammonia levels.
Good question on the ADA AS and ammonia. Not sure on this but I'm guessing that the AS is saturated with nutrients including ammonia before it is bagged up and sold. So when you add it to your tank the excess then leaks out. Amano won't disclose what he does.
The CEC substrate exchanges H+ ions for cations in the water. It doesn't really absorb anything as such. H+ ions are basically acid which is why pH drops. Also the H+ ions being acid will reduce the KH.
Don't know for sure why it's better for plants but probably because of incresed nutrient level for the roots and also perhaps of increased nutrient movement around the roots. The cations aren't locked away as such but can be removed by the plants.