# Tropica Plant Growth Substrate Lifespan



## jameson_uk (1 May 2019)

Typical aqua soil has a high CEC which gets used up (particularly with my hard water) but what about Tropica Plant Growth substrate?

Does this have a lifespan or will it continue to absorb nutrients from water forever?


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## Keith GH (1 May 2019)

jameson_uk

On average I think it's quality life span is around the 18-24 months.

Keith


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## Zeus. (1 May 2019)

If your Dosing ferts in excess it should recharge, it all depends if the granules break down into smaller granules/dust then the flow around them will be reduced which will affect the CEC as it will be effectively clogged up


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## Tim Harrison (1 May 2019)

I should imagine it behaves like any other soil, in that it depends on what you cap it with, whether you water column dose etc. I haven't used it in an aquarium so I can't say for sure.
But if it's just used as a growing medium in conjunction with additional water column dosing, and capped with fine gravel about 2-3mm it should last almost indefinitely.


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## dw1305 (1 May 2019)

Hi all, 





jameson_uk said:


> Does this have a lifespan or will it continue to absorb nutrients from water forever?


All active substrates will stop being "active" after a while. They don't lose the ability to exchange cations, they've just reached an equilibrium point with the tank water.





jameson_uk said:


> Typical aqua soil has a high CEC


That is the real point CEC is "Cation Exchange Capacity" and that is exactly what it is, the <"ability to retain and exchange cations">. 

When you start with something like <"Akadama"> or <"sphagnum peat">, all the cation exchange sites are initially filled with a proton (H+ ion), because they have formed under conditions of high rainfall. These will then be exchanged for more strongly bound multivalent cations from solution (your tank water). 




 

If you start with a "blank slate" substrate you can load it with cations by soaking it in a strong solution of ions, I assume this what ADA do when they make <"ADA Amazonia">. 

The first time I used the moler clay "Tesco Cat Litter" I rinsed it in our tap water (hard about 18dGH/dKH). It didn't get rid of the smell, and it meant that all the exchange sites were filled with Ca++ and HCO3- ions, so it raised the pH and hardness of the <"rain-water tanks I used it in">. 

If I'd used it in a tank with our hard tap water, it wouldn't have had any additional effect effect, because the ion exchange sites would already have been in equilibrium with the water.   

The next time I prepared cat litter I just left it outside in the rain for ~ six months. I could have soaked it in an acid solution (acids are defined as "H+ ion donors"), but I would also have added anion. 

If I try it again I might have a go with hydrochloric acid (HCl) first, followed by some time (couple of weeks?) in the rain and see what happens then. 

cheers Darrel


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## Zeus. (1 May 2019)

dw1305 said:


> If I'd used it in a tank with our hard tap water, it wouldn't have had any additional effect effect, because the ion exchange sites would already have been in equilibrium with the water.



 Never thought about that  but it makes sense the sites for exchange get blocked with ions that have higher ionic bonding than the ferts ions, so if your water is hard enough I suppose your AS could end up being similar to an inert substrates.

So WC dosing is more important in older tanks with AS

Another nail in the coffin for hard water and a good point why soft water and growing plants makes sense!


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## dw1305 (1 May 2019)

Hi all, 





Zeus. said:


> sites for exchange get blocked with ions that have higher ionic bonding than the ferts ions, so if your water is hard enough I suppose your AS could end up being similar to an inert substrates


Yes, that is it. 

The only way of getting the substrate to release the ions it has bound would be to put it in a strong solution of another ion. If you have a high enough concentration of ions in solution the differential between the substrate and water will mean that a less strongly bound ion (like sodium Na+) can replace a more strongly bound ion (like Ca++). 

This is why you can re-charge ion exchange resins for water softeners etc in a strong brine solution. Via <"Wikipedia"> 





> Water softeners are usually regenerated with brine containing 10% sodium chloride.[4] Aside from the soluble chloride salts of divalent cations removed from the softened water, softener regeneration wastewater contains the unused 50 – 70% of the sodium chloride regeneration flushing brine required to reverse ion-exchange resin equilibria.


cheers Darrel


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## jameson_uk (1 May 2019)

dw1305 said:


> Hi all, All active substrates will stop being "active" after a while. They don't lose the ability to exchange cations, they've just reached an equilibrium point with the tank water.That is the real point CEC is "Cation Exchange Capacity" and that is exactly what it is, the <"ability to retain and exchange cations">.


I don't believe this is active (https://tropica.com/en/plant-care/substrate/k.  This is the fine soil stuff that goes down as a 1cm base layer and you cap with gravel.

I do have some of the Tropica Aquarium soil which is active in my shrimp tank but I think it's now simply an inhert substrate.


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## Matt @ ScapeEasy (12 May 2019)

Bump! Be interested to see members views on the lifespan of the tropical substrate (as jameson_uk has rightfully pointed out, this is the one that goes underneath as a base layer)...


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## Cédric (18 Mar 2022)

dw1305 said:


> All active substrates will stop being "active" after a while. They don't lose the ability to exchange cations, they've just reached an equilibrium point with the tank water.


Hi Darrell,
Can you tell us more about this equilibrium ? Does it means concentration of cations are same in soil and water ? Do you have an example ? I'm still trying to understand how things work.


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## dw1305 (18 Mar 2022)

Hi all, 


Cédric said:


> Does it means concentration of cations are same in soil and water ?


It does. Have a look a the <"Lenntech pages on ion exchange">.


Cédric said:


> Do you have an example ? I'm still trying to understand how things work.


It is usually where you have hard water, saturated with calcium carbonate (CaCO3) as Ca++ and HCO3- ions.  At 420 ppm CO2 that is about 17dGH / 17dKH.

If you just look at cations, those Ca++ ions will be exchanged for any less strongly bound ions, dependent on both <"the lyotropic series"> and their concentration in the tank water. 

Once all the exchange sites have a strongly bound Ca++ ion (and are continually bathed in a solution rich in Ca++ ions) there isn't any further exchange. It is the same reason <"that a limestone rock (or snail shell)"> won't dissolve in hard water.

cheers Darrel


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## Cédric (19 Mar 2022)

dw1305 said:


> Once all the exchange sites have a strongly bound Ca++ ion (and are continually bathed in a solution rich in Ca++ ions) there isn't any further exchange. It is the same reason <"that a limestone rock (or snail shell)"> won't dissolve in hard water.


The soil will remain a nutrient reservoir for the plants but does it lose the power to lower the KH when equilibrium is found ?


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## dw1305 (19 Mar 2022)

Hi all, 


Cédric said:


> but does it lose the power to lower the KH when equilibrium is found ?


Yes it does. 

The substrate doesn't have any H+ ions (protons) to exchange (~ all the cation exchange sites have a Ca++ ion). Acids are "proton donors" and the substrate has stopped acting as a weak acid buffer. 

cheers Darrel


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