# CEC of non-traditional subtrates?



## FishFarmer (Feb 8, 2007)

CEC stands for Cation Exchange Capacity. All it really is, is a measure of a soil's ability to retain cations. A higher CEC is a good thing, because it means you can retain more cations, and many cations are plant nutrients.

CEC in a soil can come from: organic matter (that's where the majority of CEC comes from in most soils), hydroxides and oxides (they add very little to the CEC), and clays (a large source of CEC in soil). As you said, Eco and Flourite are derived from clays, so logically they should have a high CEC--but they don't. As a matter of fact, their CEC is horrible.

The reason is the heating. CEC in clays is a result of an anion being substituted into the inner lattice structure of the clay during it's formation, resulting in a negative charge on the clay (call isomorphic substitution). Many clays also have water trapped in between their layers, which expands the clay and allows cations to bind to the sites where the anion substituted (this would be CEC!). Now, when you heat things, you cause them to expand, in this case, the layers of the clay expand and the water and anions in the inner layer of the clay leave, and when the clay cools down, the layers collapse. Now all the anions that gave the clay the high CEC moved out, and they also cannot get back in because the water is gone and the layers have collapsed, thus eco and flourite have crappy CEC.

Lesson of the whole story, if you want a substrate with high CEC, don't use Eco or Flourite.


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## driftwoodhunter (Jul 1, 2011)

LOL - I had to laugh - I was going to respond by saying "after I read it twice..." and then you posted it twice : )

Thank you for the clear-cut explanation. I was thinking that baking the clay or brick is what created the high CEC - I though it had to do with porosity, not ions!
So, does clay with anions draw nutrients to itself, and it requires water within the clay to create the cation? Do I correctly understand that the clay needs both the anion and the water for the cation, resulting in a high CEC? Is this only naturally occuring, or is it man made/created?
What is a good CEC substrate?
Thanks for the lesson!


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## mistergreen (Dec 9, 2006)

yes, on any baked clay including bricks. The problem is crushed bricks and such will produce irregular sizes, sharp edge, and takes lots of work... It's a lot easier to buy.


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## Steve001 (Feb 26, 2011)

driftwoodhunter said:


> (vs. white clay or porcelain, because I've read the red clay is higher in iron, that's why it's red! lol)


Not true.


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## DarkCobra (Jun 22, 2004)

driftwoodhunter said:


> What makes the expensive packaged stuff so much better, or is it maketing?


Marketing it for a planted aquarium makes it expensive. Otherwise, it can be cheap.

For example, Turface Infield Conditioner is about $20 per 50lbs. Since it's light, it goes a long way per pound. It's also repackaged as Schultz Aquatic Plant Soil, and a PondCare product; both made for outdoor ponds and less expensive than aquarium substrates.

There are various other products too, like bonsai-grade expanded shale (Haydite). Also cheap if you can manage to find it locally and avoid shipping.

Both Turface and Haydite are fired to high temperatures to make them stronger, because they are expected to last for many years in their intended applications. So they will last many years in your aquarium too, without breaking down into mud and clouding the water. And they still have acceptable CEC.

I have grown plants in both Turface and the now-discontinued Soilmaster Select (SMS) with great success, including carpeting plants. Excellent growth and massive root networks compared to inert stone substrates.

While some softer (and shorter-lived) aquarium substrates have much higher CEC, or may release their own nutrients for a year or two, I don't believe this produces proportionally better results; and certainly isn't necessary. I'd rather have a substrate that will last, and provide consistent results for five years like my SMS has.

Speaking of crushed brick, I have a sneaky suspicion that's what Hydrophyte's Ion Plant Gravels are.


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## driftwoodhunter (Jul 1, 2011)

:redface: It was his posts that got me thinking...

but if the alternate substrates are fired clay, does that significantly lower the CEC? That was my impression from the first (2) replies ; )

I may be able to locate the bonsai medium, there are a few nurseries here that sell bonsai supplies.
I'm looking for a substrate that will retain nutrients fed through the water column (I also use osmocote caps) that won't break the bank - I have limited resources and now I'm setting up two 29s with a combo of laterite, FloraMax, MGOCPS, and a cap, probably pea gravel but I haven't decided yet. I'm just wondering what else is out there other than the typical things mentioned on this site.
You just gave me two items to look into...


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## DarkCobra (Jun 22, 2004)

driftwoodhunter said:


> but if the alternate substrates are fired clay, does that significantly lower the CEC? That was my impression from the first (2) replies ; )


But what is considered significant?

Let's say that FishFarmer is comparing the CEC of fired clay products to the highest CEC material, being organic material in soil. That's really not a fair comparison, but I think that's what he's doing, so let's roll with it anyway.

Turface has a CEC of about 30 (already _much_ better than sand, at only 2.5).

The highest CEC organic material I could readily find a number for is peat moss, at 106.

So the peat moss would appear to be 350% better.

Or would it? Does that actually result in 350% better growth and health? A plant's growth is ultimately limited by other factors, like light and CO2; not just the nutrient supply. And health... well, you can't exceed perfect health, and can get close to that easily enough just by supplying minimum requirements. Bigger root mass maybe? Probably a good thing up to a point, but beyond that it's just overkill; who wants a plant that's half roots? :hihi:

Given that, and taking your personal expectations and preferences into account, I'm sure you can come up with your own interpretation of what's significant.


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## Hoppy (Dec 24, 2005)

The highest CEC I have seen listed for a material that would work as a substrate is for Zeolite sand, used for pool filter sand. I tried some once and it wasn't any improvement I could see over ordinary pool filter sand. But, I have no doubt the a good CEC makes a substrate more effective at growing plants. What a good CEC is, I don't really know.


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## Robert H (Apr 3, 2003)

> Lesson of the whole story, if you want a substrate with high CEC, don't use Eco or Flourite.


Where are you getting that information from? Clay gravel of any kind does have relatively high CEC. Some types of clay have extremely high CEC. People haven't talked much about CEC in the forums for years, but back in the 90s it was all the rage. Flourite is low compared to other clays. Eco complete hasn't been included in any studies I know of.

Jamie Johnson of the Aquatic Gardeners Association did a very detailed study of aquarium substrates analyzing both mineral content and CEC level. If you read his study, take a look at the chart and the exact CEC measurment of each planting medium. It was last updated in 06.

http://home.infinet.net/teban/jamie.htm

Any porous medium has CEC capability. Aquarium gravel has zero in part because it is usually epoxy coated. Clay gravel is not epoxy coated. Zeolite, perlite, and vermiculite have the highest CEC rates of any medium but are generally not used in the aquarium, with the exception of zeolite. Sand has very low to zero CEC. 

Just because a medium is high in CEC does not mean it contains any minerals. It only means it has the ability to absorb minerals, (cations) that are present in the water. Peat is also very high in CEC, but does not contain minerals and as it decays can cause problems. Despite the dangers of using peat in the aquarium, small amounts not only provide CEC, but the acid from decomposition makes oxidized minerals water soluble.

"Calcined clays - clays that are heated to a high temperature to cause an extreme hardening and oxidation. They can then be fracted into smaller pieces to be used as a primary substrate base. They become very porous on firing, and provide many nutrient binding sites. Chemically and physically stable. Good CEC." This includes Eco complete, Turface, Soilmaster, Schultz clay conditioner, Schultz/Profile Aquatic Plant soil... and other similar products. Some products like Eco complete add things like live bacteria and binders that make the oxidized minerals of the clay more readily available, (turning Fe+3 oxidized iron into water soluable Fe+2 iron)

"Fuller's earth -(Schultz, Profile, Turface) porous, colloidal aluminum silicate clay mineral that lacks plasticity and is often used as an adsorbent, folter medium, and a carrier for catalysts. High adsorptive power. Grey to yellow color. Good CEC."

The benefit/effectiveness of CEC in the aquarium has always been difficult to measure, but it has always been assumed that more is better.


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## plantbrain (Dec 15, 2003)

Clay loams have very high CEC, eg rice paddy soil or ADA AS etc.........
They also have more nutrients that are bioavailable.

Bit messier than Hard sands etc........

But offer more to the plants.

Potting soil is a bit more larger and more OM, and less clays..........but works well too.

Compost can vary.


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## FishFarmer (Feb 8, 2007)

Robert H said:


> Where are you getting that information from? Clay gravel of any kind does have relatively high CEC. Some types of clay have extremely high CEC. People haven't talked much about CEC in the forums for years, but back in the 90s it was all the rage. Flourite is low compared to other clays. Eco complete hasn't been included in any studies I know of.


Yes, I realize that all clays have decent CEC, but when they are fired in a kiln, you are essentially altering the molecular structure of the clay, thus reducing its CEC. Clays have a high CEC because of the isomorphic substitutions and the incredible surface area of clays (some clays have up to 800 square meters of surface area per gram of soil!)

That link you provided is where I remember looking up the CEC for Flourite, and as you can see, it is rated at 1.7meq/100g. That is not very good as far as I'm concerned. I've never seen an exact measure for Eco, but I would guess it would be somewhere around the same as Flourite. But, I guess relatively speaking, Flourite and Eco are some of the better substrate choices for CEC when compared to gravel or sand.

As for a good substrate that would have a high CEC, the only really good one would be mineralized topsoil--but even topsoil is highly variable (depends where it's from and under what conditions the soil formed). Trying to find a really high CEC substrate for aquariums is a crap-shoot if you ask me.

And sorry about the repeat posts :icon_lol:. IDK how that happened


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## Robert H (Apr 3, 2003)

but you are mistaken, firing the clay actually raises the CEC, and when its fracted into small pieces, that raises it more. That is shown in the study- and Jamie explains this in the study. Schults/Profile is one of the highest CEC of all the mediums tested, and it is kiln fired and fracted.


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## FishFarmer (Feb 8, 2007)

That is interesting, because I recall reading a paper where heating a clay decreased the CEC, and I remember my soils professor taking about heating clays and reducing CEC. And I agree with you, fracturing any clay would increase it's CEC because you are increasing its surface area--I don't think there's any debating that point.

I do suppose however, that the type of clay would influence whether heating would increase or decrease CEC. I could see that heating a 1:1 such as kaolinite could increase the CEC since it has no inner layer that could collapse. But I still don't see how heating a 2:1 clay, especially a hydroxy-interlayered clay like smectite, would increase its CEC since a majority of its CEC is directly due to cations being able to access the inner layer of the clay--and if that inner layer collapses than those CEC sites are no longer available to bind a cation.

I'll see if I can dig up some literature on this.


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