# Substrate CEC Analysis / results



## Quagulator (May 4, 2015)

After researching, gathering data and a recent discussion on cation exchange capacity (CEC) found here: http://www.plantedtank.net/forums/2...alysis-lab-work-hold-now-full-discussion.html

I have put together some results of CEC ratings from various planted tank substrates. Before I dive into those, I should disclaim that I have no bias towards what substrates anyone uses, if it works for you, fantastic, there is no “one size fits all” substrate in my opinion. I think we have all seen absolutely stunning planted tanks regardless of which substrate was used! I should also disclose that by no means are these CEC ratings a definitive answer to “what substrate is best.” I simply wanted to put some values to the CEC discussions I am seeing all over threads, regardless of which forum I was reading. Some of this is my educated opinion, so remember that when reading, feel free to correct me or discuss any matter you feel necessary.

What is CEC – CEC measures the amount of nutrients, more specifically positivity changed ions, a substrate can hold onto/store for future plant use, the most common being potassium, calcium and magnesium. The CEC rating is generally shown in milliequivalents per 100 grams of substrate (meq/100g). The higher the number, the higher the CEC. 

What contributes to CEC – Generally organic material (OM) and clay content are the greatest contributors to substrate CEC. So as the OM and clay content increase, so does the CEC. This puts sandy substrates on the low end, and clay substrates on the high end. 

Surface area – Higher surface area generally results in a higher CEC. The more surface area there is, the more potential bonding sites there is along the CEC. This is where the results below are interesting, clay based, planted tank substrates have a very poor rated CEC. 


Results:

Organic potting soil sources:
humus - 200 
vermiculite - 150 
sphagnum peat moss - 100 - 200 
fine clay soils - 55-65 
2:1 v/v) barkerlite - 24 
(1:1 v/v) peat:vermiculite – 141

Tripepi, R. R. (2014). What Is Your Substrate Trying to Tell You Part II.
https://www.extension.uidaho.edu/nursery/Landscape problems/Substrate/CEC and CN ratio.PDF

Common planted tank substrates:
Special Kitty Cat Litter – 27
Seachem Fluorite – 1.7
Seachem Onix – 1.3
Caribsea Tropic Isle Laterite (similar to eco-complete) – 6.7
Calcined Montmorillonite Clay (Safe-T-Sorb) – 30-40
Play Sand - < 0.1

Johnson, J. S. (2000). Substrates for the Planted Aquarium. Planted Aquaria. 17-23. 
http://sfwcf.com/pam/pam2c.pdf

Substrates for the Planted Aquarium

Assumptions:
ADA Aquasoil/other related substrates – Because this is likely formulated from organic matter, clay and binding agents, we can expect a high CEC. I have read on various posts claiming this product is similar to rice paddy soils resulting in a CEC rating of 50 meq/100g. I would take this one step further given the true, tested CEC rating of organic matter mentioned above. I believe a CEC rating of 50-100 meq/100g would be more suitable. 

Blasting Sand/Pool Filter Sand – Assuming CEC rating of <0.1 meq/100g (estimated via play sand rating)

Discussion: 

As you can see, a dirted tank should have the highest CEC, so is “burning out” a dirted tank a myth? I think we aren’t feeding the CEC of the dirt, so eventually is will burn out. Feed the dirt folks!! 

Fluorite and Eco-Complete style soils have poor CEC ratings: If we look at the physical structure of these substrates, we can see that there is lots of “room” between each granule. This corresponds to lots of macro pores which bring the CEC rating per 100 grams down: there is no CEC in macro pores, so more macro pores per 100 grams of sample will result in a smaller CEC rating. But, looking at the product page on each of these substrate’s websites, they don’t claim a high CEC, I think us as hobbyists adopted the term because the materials these substrates are made of are thought to have a high CEC. Not the case. 

So, what can these macro pores offer? Well, anyone with Fluorite/Eco-Complete, go look at your tank and you’ll see lots of detritus and mulm that occupies these macro pores. The detritus/mulm is slowly being broken down into plant available compounds via our microorganism populations. This can be compared to a CEC because the CEC stores plant available nutrients to be released at a later date, while decomposing detritus/mulm is simply stored nutrients being released at a later date via the decomposition process. This is however, not as sanitary as proper stored plant available compounds in the CEC from let’s say, dry fertilizers. As the organics decompose, this drives up TDS, releases non-plant usable compounds, could drive algae growth, could cause high point sources of nitrates and generally fouls the water more so than supplying plants with traditional fertilizer. Of course, lots of these compounds can be stored in the CEC, but many are released into the water column. It is my belief that CEC in the planted aquarium will fill up rather quickly, and be of little use, instead we mistake the CEC for decomposing organics within macro pores in our substrate. 

What about “heavy root feeders?” – While this is a hot/touchy subject, heavy root feeders in my mind are plants that are simply better suited/more efficient at taking up nutrients via their roots instead of shoots/leaves. There will be root interception of both detritus/mulm/root tabs and CEC nutrients, but I believe mass flow and diffusion from water (both above and below the substrate) is the main way of nutrients getting into our plants. So in theory, detritus/mulm/root tabs would have to be released into the water to be up taken into the plant. Some of the nutrient dense water will remain within the pores of the substrate, easily taken up through roots, while lots will leach into the water column. For this reason, I believe it is too complicated to place a term such as CEC as being a sufficient single source of nutrients for plants. 

Overall, the CEC of planted tank substrates in my opinion, is an over estimated source of nutrients, and really shouldn’t be praised when talking about substrates. The bulk nutrients our plants use are likely leached into the water column anyway, with the CEC remaining maxed out at all times. If you skip fertilizing, I believe the decomposition of detritus/mulm is a larger source of “stored” nutrients than the CEC of your substrate. High CEC of course helps and is useable, but within aquaria is it only a small building block of nutrient availability.


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## madcrafted (Dec 23, 2017)

Quagulator said:


> The detritus/mulm is slowly being broken down into plant available compounds via our microorganism populations. This can be compared to a CEC because the CEC stores plant available nutrients to be released at a later date, while decomposing detritus/mulm is simply stored nutrients being released at a later date via the decomposition process. This is however, not as sanitary as proper stored plant available compounds in the CEC from let’s say, dry fertilizers. As the organics decompose, this drives up TDS, releases non-plant usable compounds, could drive algae growth, could cause high point sources of nitrates and generally fouls the water more so than supplying plants with traditional fertilizer.


Good point. Nutrition may not be lacking but the high organics in the water column is most likely giving many of us with such substrates issues with algae. This effect can me more problematic in smaller volumes of water, like my 5 gallon tank. Couple that with a dirty filter (which will be sooner than later with smaller filtration devices) and you have a recipe for algae blooms. 

I can attest to this as a user of Eco complete. I have to clean my filter at least every other week and would probably be better off doing this every week. My spec v has a weak mechanical filter but serves well as a biological one. However, if mulm, detritus, etc. is being built up to the point where the bacteria can't consume it fast enough, this can be a real issue with keeping a clean water column. 

Food for thought. I doubt I'll use the stuff again. Not only for this reason but for the difficulty of keeping delicate plants anchored down until they take root well. My Amano shrimps also make a mess of this stuff. They just toss pieces around like they intentionally want to wreck my scape. lol


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## roadmaster (Nov 5, 2009)

Quagulator said:


> After researching, gathering data and a recent discussion on cation exchange capacity (CEC) found here: http://www.plantedtank.net/forums/2...alysis-lab-work-hold-now-full-discussion.html
> 
> I have put together some results of CEC ratings from various planted tank substrates. Before I dive into those, I should disclaim that I have no bias towards what substrates anyone uses, if it works for you, fantastic, there is no “one size fits all” substrate in my opinion. I think we have all seen absolutely stunning planted tanks regardless of which substrate was used! I should also disclose that by no means are these CEC ratings a definitive answer to “what substrate is best.” I simply wanted to put some values to the CEC discussions I am seeing all over threads, regardless of which forum I was reading. Some of this is my educated opinion, so remember that when reading, feel free to correct me or discuss any matter you feel necessary.
> 
> ...


From the first paper you submitted high lighted in blue above^
"The higher the CEC the better the mediums ability to hold added cation's which ultimately improves potential for plant growth."
Believe most folks are interested in improved plant growth.
you can read till the cows come home and offer opinions' but as a wise man once said "try,do,then speak.


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## Quagulator (May 4, 2015)

roadmaster said:


> From the first paper you submitted high lighted in blue above^
> "The higher the CEC the better the mediums ability to hold added cation's which ultimately improves potential for plant growth."
> Believe most folks are interested in improved plant growth.
> you can read till the cows come home and offer opinions' but as a wise man once said "try,do,then speak.


While this is certainly true, in our aquatic environments nutrients that aren't bound in the CEC are still within the water column, still available to plants. In terrestrial environments, we would could loose these to volatilization, leaching, erosion and runoff so yes, higher CEC will always result in improved nutrient availability. In our tanks, the nutrients can't really go anywhere... Except changing water where we replace most of the cations like Ca and Mg anyway... Even substrates with high CEC ratings are more than likely full to the brim at all times because of the constant addition of organic matter via fish waste, food etc.... and because Ca and Mg are quite prevalent in our tap water, in theory the CEC is likely completely made up of Ca and Mg. Most other nutrients are not bound into the CEC and therefore the efficiency and practicality of CEC in planted tanks is reduced. 

I'm not sure what you mean by "try, do and then speak".... I simply researched tested CEC values, and offered my opinion on a few aspects regarding CEC and growing plants in a fish tank.


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## roadmaster (Nov 5, 2009)

As mentioned in your other thread where this should also be in my view.(less confusion)
Testing for ones self is simple.
Believe most high dollar substrates designed for aquarium's rely on CEC to help hold whatever they infuse into the mix to help plant's get off to good start.
You and I can do likewise by soaking the chosen substrate material in nutrient laden tub of water.
I would agree that in High energy tanks where nutrient dosing via water column is twice,thrice weekly,that CEC capability is of lesser importance.
But low tech,low energy tanks left to run for month's/year's can more easily appreciate soil mixes and their properties.


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## jeffkrol (Jun 5, 2013)

roadmaster said:


> As mentioned in your other thread where this should also be in my view.(less confusion)
> Testing for ones self is simple.
> Believe most high dollar substrates designed for aquarium's rely on CEC to help hold whatever they infuse into the mix to help plant's get off to good start.
> You and I can do likewise by soaking the chosen substrate material in nutrient laden tub of water.
> ...


Yea, not to sure about that..In 2 of my tanks I have flourite/rotten granite and Turface in the other..
Mod light, CO2 injection, little ferts.. in both.
See little difference in growth BUT there are a dozen other factors different for each tank....
Actually IF I needed to, I'd take the growth in the low CEC tank over the high CEC tank..

Point is I'm not sure there is good proof either way..

That said, I am planning on using my own mix of Turface, "dirt" and granite as my next tank..
Think more will have to do w/ structure and micro-organism differences than just plain CEC..

I suspect the benefit of high CEC soils is only brief..i.e establishment period.
After that root tabs or wc feeding is basically the same thing
I mean if you "naturally recharge" them in a low tech environment most of those nutrients come from either the water column (where they are already available to the plants) or the top boundry layer where they also can move "up" or down..

Of course one needs to consider size and number of water changes..

As a final thing.. it does seem my high CEC turface tank does maintain slightly lower Nitrates than the low CEC tank..
Why??????

THIS paper may help somewhat..
https://water.usgs.gov/nrp/jharvey/pdf/Oecologia_2003_422_445_501.pdf


> Several key structural components differ between aquatic
> and terrestrial systems. The ratio of elements in dissolved
> or particulate forms, the major sites for nutrient storage,
> and the stoichiometry (elemental ratios) of detrital pools
> ...


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## roadmaster (Nov 5, 2009)

Yes I agree with much ^
Types of clay's, soil's,Particulate size, interface activity, temps,O2,CO2 being produced or drawn upon (more critical than CEC), mineral make up's, (bunch of variables).
Soil/clay/peat mixes produced best result's for me in low energy tanks over the long haul.(12 to 24 month's)
CEC capabilities of substrate as mentioned, will always be of benefit to the stem plants and the higher the better.IMHO
Other's can and will debate what is best/better, and I like such discussions .
Politely disagree with those opinion's that CEC capabilities are of little value in planted tanks.
Ditto for the use of liquid carbon supplement's.
You don't know maybe ,can't see maybe, lest you've tried without both for extended period's and repeated attempt's.
Then employ both, and the difference is more noticeable.
Only my observations and they carry no more,no less importance/weight than other's I choose to respectfully disagree with.


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## Quagulator (May 4, 2015)

I'll have to agree on using a dirt/clay/lava rock mixture, I myself am more interested in the structure and microorganism activity over the CEC provided by organic matter and clay. That is the mix I will be using on my next tank. As for fluorite/eco-comp substrates, both of the TESTED CEC values are very low.... but yes, soaking them in nutrient rich solution would be of initial benefit when setting up a new system. I've actually been using recycled/seasoned fluorite as a base layer in most of new new setups.. not realizing it's CEC rating is only 1.7 meq/100g.


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