# Tropica quote



## beeky (22 Nov 2007)

I've just noticed that on AE for the description of Tropica Plant Substrate, there's the line "Removing nutrition from water reduces the risk of undesirable algae growth".

Anyone else noticed this?


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## Tom (22 Nov 2007)

So what happens if you use Plant Nutrition?? Does it suck it all up?


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## beeky (22 Nov 2007)

That's what I thought!

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).


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## George Farmer (22 Nov 2007)

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.


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## ulster exile (22 Nov 2007)

But then why use a substrate like that?  

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!


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## JamesC (22 Nov 2007)

beeky said:
			
		

> "Removing nutrition from water reduces the risk of undesirable algae growth".


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.

James


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## Themuleous (22 Nov 2007)

Fascinating James.  I assume NH3 is negatively changed then and therefore gets released from ADA AS creating the spike when first used in a tank?

When you say this



> the KH drop is not, as some believe, the substrate absorbing HCO3, CO3.



Why does the KH drop then?  Due to the decrease in pH caused by H ions?

Also, how is this process beneficial to the plants?  If the nutrients are locks into the substrate they can't get them?  Or is this were the plant root micro hairs come into play?

Sam


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## JamesC (22 Nov 2007)

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.

James


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## Themuleous (22 Nov 2007)

Right oh, cheers James


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## fishgeek (25 Nov 2007)

plants are able to utilise the bound fertiliser/nutrients through active process or chenical reactions in root nodes
algae cant do these reactions

so the high CEC acts as a store of nutrients so that if something isnt dosed regulalry, then the substrate mops up the excess and holds it for higher plants to utilise at a latter date

or thats my understanding
andrew


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