# Is CEC levels really that important??



## JButera

I can see how a high CEC substrate would make sense when used with terrestrial plants due to rain, irrigation, soil erosion..etc etc, but with a fish tank idk. Seems to me that the nutrients are already trapped within the fish tank anyway.


----------



## Guck

If you could remove all the cations out of the water column and place them in the substrate for one thing, what do you think would happen to algea growth?
That's one thing high CEC substrates do. The cations being held in the soil makes it lots easier to be used by the roots. Assuming roots are in the soil obviously.
That can also be beneficial to the fishes who may not tolerate (read not be so happy) certain level of some nutrients.

You should get a hold of Diana Walstad book, Ecology of the planted tank. It's a good reference.


----------



## Michael

Agreed. The point of having a high cation exchange capacity (CEC) substrate is to hold nutrients in the substrate where plant roots can absorb them and where they are not available to algae.


----------



## Diana K

Also, held in the substrate, they are still there when you do a water change. If your plants are not using the water column ferts as fast as you add them, you are building up a reserve so that when you go on vacation, or otherwise stop dosing, the plants are just fine.


----------



## JButera

I see your point on algae growth but what about people that dose ferts on a daily basis? I emailed Seachem about this and their response was that high CEC substrates are basically overrated. Here's a quote from Seachem; "CEC has somewhat of a negligible contribution to the success of planted aquarium systems, and it is not really a good indicator of the success one will have with a substrate, but take that as you may 😃". This was all in reference to flourite and it's relatively low CEC. *This was original written in response to Guck's post*


----------



## Guck

It is true that using a substrate with high CEC does not guarantee success. On the other hand Seachem is in the business of selling ferts... the more you use the better for them. They would want everyone not to use high CEC substrate. This way the soil cannot build reserve as pointed out by Diana.

Sent from my SGH-M919V using Tapatalk


----------



## Seattle_Aquarist

JButera said:


> I see your point on algae growth but what about people that dose ferts on a daily basis? I emailed Seachem about this and their response was that high CEC substrates are basically overrated. Here's a quote from Seachem; "CEC has somewhat of a negligible contribution to the success of planted aquarium systems, and it is not really a good indicator of the success one will have with a substrate, but take that as you may &#128515;". This was all in reference to flourite and it's relatively low CEC. *This was original written in response to Guck's post*


Hi JButera,

Welcome to APC! I have used high CEC substrates for the last six years. Prior to that I used a natural inert gravel. Growth with high CEC substrates is definitely much better.

I like Seachem products, and still use them as part of my fertilizer dosing regime. That said if I sold Flourite with a CEC=1.7 and a price of 15# for $21 verses a montmorillonite clay substrate with a CEC=29 to 41 and a price of $6.49 for 40# then I would probably downplay the value of high CEC substrates as well. FYI, ADA Aquasoil such as Amazonia has a very high CEC as well.

20 gallon with Safe-T-Sorb #7941 substrate


----------



## Zapins

JButera said:


> I see your point on algae growth but what about people that dose ferts on a daily basis? I emailed Seachem about this and their response was that high CEC substrates are basically overrated. Here's a quote from Seachem; "CEC has somewhat of a negligible contribution to the success of planted aquarium systems, and it is not really a good indicator of the success one will have with a substrate, but take that as you may &#55357;&#56835;". This was all in reference to flourite and it's relatively low CEC. *This was original written in response to Guck's post*


I more or less agree with this statement. High CEC seems like it should make sense, but at some point the soil becomes saturated with nutrients and cannot absorb more. In fact, some toxins are bound up by things with high CEC, so it may even work against plant health to have high CEC substraits, constantly concentrating things in the substrate.

The carbon we put in our filters has an extremely high CEC rating, far higher than any substrate we use and look what that does - concentrates toxins and medications out of the water. Then after a few hours/days/a week it is full and must be thrown out.

I don't think high CEC substraits are totally useless, but I don't think it will make or break a tank. It certainly isn't a major factor in a tank's success.


----------



## Marcel G

Seattle_Aquarist said:


> Growth with high CEC substrates is definitely much better.


While I don't want to question your experiences with high CEC substrates, as far as I know, the CEC means "cation exchange capacity", so a substrate with high CEC has a high capacity to adsorb cations. And what cations? Mainly Ca+2, Mg+2, K+, Na+, and in a small amount NH4+ and Fe+2/Fe+3 also. So what a substrate with high CEC will do in our tanks, is to remove Ca+2, Mg+2, and K+ from the water column. The problem is, that the prefered place for all these nutrients is water column. See the book by Diana Walstad (Ecology of the planted tank), where she states this very clearly. If you remove Ca+2, Mg+2 and K+ from water column (which is exactly what the substrate with high CEC does), aquatic plants will suffer, and some of them may even die, because they need these nutrients in water column (not much in the substrate). Other nutrients (anions) like NO3-, PO4-3, etc. are "expelled" by these substrates, and won't stay in it. This is the reason why ADA Aqua Soil Amazonia is leaching NH4+ after you flood it with water. The NH4+ ions won't adsorb to it as easily. Nitrogen, in general, is very hard to keep in the aquatic substrate. The best way is to use Osmocote or similar fertilizer with slow release time. Also, another think to consider, the substrate with high CEC contains usually quite high amount of organic matter which may contain quite high amount of hydrogen ions (H+). This will cause a rapid decrease of pH (again, as with ADA Amazonia). And this is not ideal.


----------



## JButera

so if what your saying is correct, then what's the use of using soil? I just started my first dirted tank and tbh I really hate it.


----------



## Marcel G

According to D.Walstad, the average soil contains:
40,000 ppm (mg/kg) Fe
20,000 ppm C
15,000 ppm Ca
14,000 ppm K
5,000 ppm Mg
2,000 ppm N
1,000 ppm Mn
800 ppm P
700 ppm S
90 ppm Zn
30 ppm Cu
20 ppm B
1 ppm Mo.
Most of the Fe content is in the form that is not available to plants, but still there is more than enough iron for many, many years.
Calcium (Ca), Magnesium (Mg), and potassium (K) are usually in quite high amounts in every soil, but aquatic plants seem to prefer the uptake of these nutrients from water column rather than from substrate. So high CEC is of no (or little) use for us.
So although plants can take part of these elements up from the substrate, the prefered uptake site is water column. This also means that Ca+Mg+K content in the substrate is not that important for us (= for aquatic plants).
In organic matter there is some organic nitrogen, which by decomposition become available to plants (but anorganic nitrogen is another story => again high CEC is of no use with regard to NO3-). The same applies for phosphor (P) also. 
The elements that are there in quite high amounts are microelements.
So the main advantage of using soil in our tanks is the presence of microelements + some macroelements also (like C, P and organic N/P after decomposition). The advantage of soil is that is contains a small amount of organics (about 5%), and the organics is where most of the nutrients are stored and released.
The microelements reserve should be enough for many years. The organic N should also last a couple of years.
In case you have some fish in your tank, many N and P should be available to plants from them (and from the fish food also).
So in case you use "soil + fish + fish food" in your tank, your plants should be fine in most cases.
Maybe you can add a little CO2, as this can be the most deficient element in planted tank (but 7-10 ppm should be more than sufficient for a good plant growth).
There is some crazy thinking about nutrient demands of aquarium plants these days.
Many people think that if they are not adding 30 ppm NO3, 3 ppm PO4, 20 ppm K, and 0.5 ppm Fe, their plants will suffer defficiencies.
The truth is that most aquatic plants should do just fine with no more than 5 ppm NO3, 0.5 ppm PO4, 0.05 ppm Fe, etc.
And these values applies in case you use just water column as the sole source of nutrients (in case you use soil in your tank, you can have even less amount of nutrients in your water column).

_PS: These values are based on my experiments, practice and knowledge. I don't want to concince anybody about it. If you don't believe it, ignore it._


----------



## Michael

Marcel, thanks for your very thoughtful posts. These help to explain something that I notice, my Walstad tanks tend to develop potassium deficiencies over time. My tap water is relatively high in calcium (and maybe magnesium), so water changes replenish those nutrients. (I should read the book again, LOL!)

You also very correctly point out that natural topsoil rarely has more than 5-10% organic matter. Many hobbyists start out with artificial potting soils that are 100% organic matter. I think this is the reason for many start-up problems, and why I often recommend mixing the potting soil with Safe-T-Sorb or other high CEC/low nutrient substances. Is is easier to convince people to do that than it is to persuade them to use actual topsoil.


----------



## JButera

:hail: thanks Marcel. Would you consider a sand substrate fortified with macros and micros just as effective as using soil? I'm currently running mg's nature's care potting soil mixed with turface (2:1 by volume) with a sand cap which is staining the water like crazy, even after two 99% water changes in three days the water still looks as if someone poured iced tea in it, which I despise! Is there something about soil that cannot be duplicated with sand and some quality root tabs? Plus co2 is something I'm trying to avoid, that and fert dosing.


----------



## Michael

Unfortunately, I don't think fertilized sand is as effective. There are a number of reasons for this explained in Walstad's book, and it seems to be borne out by observation.

Try using activated charcoal in your filter, or one of the other products, to remove the tanins. They wiil go away with time and water changes, but I understand why you want them gone now!


----------



## JButera

Thanks Michael, but yeah I'm really hating that dirt right now. btw I do have Diana Walstad's book, just haven't read it yet which you may have noticed. Can we talk sand and root tabs? any reason why you think it wouldn't perform as well as a soil sub? I'm starting to think 'el natural' was coined not only for the plants and dirt substrate but also for the naturally (chronic) stained water, which most of the tanks I've seen (online) have. I've already tried a sand/turface mix (1:1) which didn't work, the sand would settle to the bottom and the turface would just lay on top after any turbulence plus I'm thinking turface may not be as great or as useful as it's believed to be. So in short, what's lacking in a fortified sand mix?


----------



## Michael

Organic matter is lacking in the sand/root tabs substrate. For an example of the difference between sand/root tabs and soil, see this current thread: http://www.aquaticplantcentral.com/...rypt-growth-walstad-vs-gravel-fertilizer.html

Your problem is tannin, not soil. Try some Seachem Purigen.


----------



## Diana K

Humus is lacking in sand. 
The equivalent fine soil particles (clay sized particles) are missing in sand. 

While this thread stated off asking about CEC, then many posts suggest it is of limited value, I think it can be important. With high CEC substrate, the fertilizer supply is more even. You could set up a tank with rather low water column ferts, as long as there is a reasonable supply of ferts in the substrate, held in a way that plants can get them as needed. CEC does this. 

Most of my tanks are finer substrates, a lot of them are montmorillonite clays- Safe-T-Sorb, Soil Master Select, Turface. 
I have several tanks with pool filter sand, Eco Complete and a few others. In general the finer materials, the clay based products have better growth. 

I am sporadic about adding ferts. So, for my way of growing aquatic plants, a substrate that will hold onto some of the fertilizer for release on demand works best. 

Yes, a blend of any of the montmorillonite clays with any heavier material (sand, gravel, Eco Complete) will separate over time. I can see the aesthetic value of using sand, gravel, larger pebbles and rock, but part of my maintenance time is spend separating the substrates, removing the Turface from the sand path, for example, or pulling the pebbles back up into visible range in the tanks that replicate a pebbled stream.


----------



## JButera

*Michael* Thanks for the link. No doubt the plants are doing much better in the walstad tank but once again the water looks like diet snapple. Now if we can only get those plants looking like that *and* have crystal clear water mmm. When you mentioned organic matter I'm presuming you mean humus which from my understanding is low in nutrients and very stable. Is the stability of organic matter an important factor in aquatic soil? and isn't sand just as stable? Then with the nutrients in organic matter, couldn't root tabs suffice in doing the job? Let's say API root tabs for macros and seachem for micros.


----------



## JButera

*Diana* I'm looking for is a clean fertile homogenize mix. Basically a substrate that has no bottom, top or layers. I just glanced over to my dirted tank and noticed the water level dropped a bit causing the filter to blow a hole in the sand cap, exposing the bottom dirt layer..more mess. This dirt substrate IMO is not worth all the hassles, I could only imagine what will happen after removing some well rooted plants after a few months plus it could never be removed and rinsed if needed. I agree that CEC is of some use in the well being of a planted tank, and would love to add some high-er CEC material into the mix but I can't find a material as of yet that will stay put. You like Michael mentioned humus but nobody explained why it's important or even needed. Seems like all your tanks are either sand, fert subs or some type of clay based material, are you not a fan of the 'dirt'?


----------



## Diana K

When a leaf or anything decomposes (such as in a compost pile, in the dirt or underwater) the materials are broken down by microorganisms. 
If you watched it happening, at first you would see a whole leave, then the tender parts would go away, leaving the veins, then the veins would break down. 
When you can no longer see the pieces individually, that is humus. 
It is organic matter that the microorganisms do not work on very much. It lasts a long time. 

The benefit is this: The particles are so small that they can have the same properties as clay sized soil particles. They have cationic exchange capacity. 
In the garden humus and clay soil particles bind together and make the clay soil a lot easier to work with. 
In the aquarium they hold on to fertilizers in a way that plants can get them. (Humus and clay do this in the garden, too). 

I tried soil from my garden in a tank many years ago. My soil is so fine the particles stayed suspended- too much colloidal clay. This was before I knew about mineralizing the soil, so I might try it that way, some day. The proper blend of garden soil + organic matter from the compost pile might bind the fine particles so they are still there (for CEC) yet connected into larger aggregates that won't cloud the water.


----------



## JButera

thanks Diana. I think I'm done with dirt for now. I'll try to find some other material to replace what humus would normally be contributing to a planted tank. btw here's some pics of my dirty 5.5 build.


----------



## Marcel G

JButera:


> "You like Michael mentioned humus but nobody explained why it's important or even needed."


Diana K:


> "The benefit is this: The particles ... have cationic exchange capacity ... In the aquarium they hold on to fertilizers in a way that plants can get them."


It seems to me that this "high CEC" thing is misunderstood. Everybody speaks of it, everybody recommends it, but nobody understands its benefits. Average garden soil has about 5-10% organic matter (or humus content), the rest are mineral particles of different sizes. The benefit of having humus in our substrate is that it contains a lot of organic nutrients. Although nutrients in organic form are not available to plants, microorganisms present in the substrate can decompose them and convert them to inorganic nutrients over time. The conversion takes some time, so it is gradual, slow. This is good. Plants thus have a constant supply of nutrients from this decomposing organic matter. Another benefit of organic matter (humus) in the substrate is that during this decomposition, CO2 is being created also. So the organics are source of CO2 also (although in smaller amounts). These are the main benefits of organics-based substrates. The CEC attribute is of no practical use for us, because as I already mentioned, the CEC means cations exchange capacity = capacity to exchange (adsorb/release) cations.
It becomes clear to you when you come to realize what cations are:
Cations: H+, Na+, K+, Ca+2, Mg+2 [NH4+, Fe+2 (Fe+3), Al+3] ...
Anions: NO3-, PO4-3, SO4-2, Cl- ...
From this it should be clear that high CEC substrate is totally useless for adsorbing N, P, S, Cl or any other anion-like ions. In fact it will "expell" all these ions. So high CEC substrate is good just for one thing: to store the excess amount of potassium, calcium, and magnesium ions. But as I said already, plants prefer to uptake all these nutrients (cations) from water column, rather than from substrate. So what's the point of storing K, Ca, and Mg in the substrate if plants won't use it much from this source? So I think that not the high CEC but rather the organic matter is what really matters.

PS: The optimal organics content seems to be 5-10%. Don't go any higher as with higher organic content a dangerous compounds may be created, or the substrate may contain too much H+ ions which will get your pH, GH and KH dangerously low.

To answer the question about root tabs vs. soil-based substrate:
I think that root tabs or any other slow-release granules like Osmocote are very good alternative for soil-based substrates with organic component (but don't forget that no CO2 will be released from Osmocote). Osmocote releases inorganic nutrients gradually in small amounts so plants can use them as they need it. The reason why the Cryptocorynes in the above comparison (http://www.aquaticplantcentral.com/...rypt-growth-walstad-vs-gravel-fertilizer.html) did not grow in the same way may have many reasons. One of it may be the lack of CO2 in the sand-based substrate. In the soil-based substrate some CO2 is being created, so I think that this may be one of the reasons why the plants grew much better in there. Another reason can be a lack of some nutrients. Root tabs may not contain all the essential nutrients, while in the organic matter there are usually all the nutrients needed. From all these reasons it is always better (safer) to use soil-based substrate whenever possible.


----------



## BruceF

The nature of water transport in plants
http://www.bio-web.dk/ole_pedersen/pdf/fb_1998_ch_12_196.pdf
Anion mobility in Soils. 
https://books.google.com/books?id=g...e&q=cation and anion in aquatic soils&f=false

Soil Chemistryby Jim Kelly. 
http://dwb4.unl.edu/Chem/CHEM869V/CHEM869VLinks/www.hallman.org/plant/soilchem.html


----------



## Michael

Bruce, thanks for the links! I will admit that the more technical parts of the articles made my eyes roll back in my head. But the general insight I got is that CEC in the substrate, presence of humus, and the ability of plants to move water from the roots and oxygen to the roots create a synergy allowing uptake of most nutrients from the substrate.

This is not explicitly stated in any of the articles, but rather a conclusion from all of them taken together. I'd like to hear others' thoughts.


----------



## BruceF

Yes Michael I tend to trip on science also often hitting my head and getting a headache but that is the gist of it. I am not sure ‘most’ is the correct word though. I think plants will take nourishment any way they can when it is hard to find and use the least energy they can when they have the opportunity. Face it if they weren’t so lazy wouldn’t they be more mobile? 

I think there are too many generalizations in this hobby in the first place. (Plant driven design! I know you know that one!) So plants with roots will do one thing and stems will do another and the floaters suck up air etc. 

I keep a 29g tank with no substrate. I’ve been doing that for years. The epiphytes are attached to wood. They do fine. The stem plants I often float or weigh down somehow they seem to do fine. Plants with roots I always put in pots with substrates, usually dirt. 

I pulled apart a tank the other day that had clay from my yard capped with sand. The crypt rootballs were solid sticky masses. The anubias had grown down into the substrate and those roots were everywhere. The stargrass on the other hand never rooted at all. It seemed to prefer to float I suppose in order to get at the co2 in the air.


----------



## Michael

Agreed. What I should have said is "rooted plants can get most of their nutrients from the substrate if that is the only place they are available."


----------



## JButera

same here Bruce, thanks for the links. Reading the second one was a real struggle though..where's Marcel when I need him?


----------



## Marcel G

JButera said:


> where's Marcel when I need him?


I was trying to discuss this topic in more detail with other knowledgeable people, so that I'm not talking nonsense here.
There's a good reading here also:
http://www.ukaps.org/forum/threads/high-cec-with-hard-water-pointless.38582/#post-419001

I have to admit that I was wrong in saying that the substrate is not exchanging anions also, but this exchange seems to be just minuscule compared with the cations exchange in the substrate. For most anions [= negatively charged ions/molecules like NO3-, PO4(3-), SO4(2-), Cl-, Br-, etc.] it is hard to stay in the substrate in the form that is available to plants. There is a lot of nitrogen or phosphorus in the substrate, but most of it is in the form that is not available to plants (i.e. as an insoluble compounds or precipitates). So the substrate (soil) contains usually all the essential elements, but mainly only the cations are there in the "for-plants-available" form (= soluble form). This means also, that if you put KNO3 + KH2PO4 into your substrate (thinking it will stay there as a nutrient reserve), most of the NO3- will leach into the water (not being able to attach/adsorb to the substrate), and most of the PO4(3-) will quickly react with iron [Fe(3+)/Fe(2+)] forming insoluble precipitates. In other words, there's no easy way to keep these anions [NO3-/PO4(3-)] in the substrate ... in soluble form that is available to (utilizable by) plants. The best solution to this problem (I know of) is to use some fertilizer with slow release rate (like Osmocote).

I was also wrong in saying that high CEC is of no use for us (for plants). Although the substrate with high CEC will attract the cations only (or mainly), and as I already said, aquatic plants seem to prefer a water column uptake of these ions [Ca(2+), Mg(2+), K+], when the water will become depleted of these nutrients, they will release from the cation-rich substrate and get into the water column, where they will be available to plants for uptake. So while the cations bound to the substrate may not be as useful for plants (as they prefer them in the water column), whenever there is less cations in water then in the substrate, there will be an "exchange" between water and substrate ions => "cation exchange" (CEC). However, I still think that in water there is plenty of Ca(2+) and Mg(2+) ions, so if we do a regular water changes we may not need such a reserve in the substrate.

Another point I was explained by someone else, is that some kind of soils contain a significant amounts of humic and fulvic acids. The humic acids have a really high CEC but they are not able to enter in the plants. They can, however, act as transporters of cations to the roots, and they improve the cation mobility in soils. The fulvic acids are much more reactive molecules and smaller than humic acids. Fulvic acids react with many trace elements and they can be absorbed as a whole by the plants, so fulvic acids are transporters of trace elements directly into the plants (like chelates).

So to put all this into practice, we can use an ADA Aqua Soil Amazonia as a good example:
ADA Amazonia is a high CEC substrate => 269 mM/kg (26.9 mM/100g). This means that this substrate can "accept" (adsorb) up to 269 mM/kg of cations.
Although I don't know the exact amount of NH4+ ions in this substrate, it is not that important to know it because the NH4+ ions have very weak bond to the substrate, so once you put this substrate into the water, nearly all the NH4+ ions will leach into water column. According to laboratory analysis I did, this substrate contains 2 mM/kg of K+, 17 mM/kg of Ca+, 3 mM/kg of Mg+ ions, which gives us a total of 22 mM/kg of cations adsorbed to the available 269 mM/kg cations sites. So we have a substrate with 269 mM/kg of free sites, and only 22 mM/kg of cations on these sites. The other sites are occupied by acidic H+ ions (cations). Now, what happens when we put this substate into our tank and flood it? Nearly all the NH4+ and H+ ions which were loosely adsorbed to the substrate will be released to the water column, and Ca(2+) and Mg(2+) will come to their place => in "exchange". So now we have a big amount of NH4+ and H+ ions in the water column, and at the same time a big depletion of Ca(2+) and Mg(2+) ions from water column. This will be reflected in the water as a significant drop of the pH (= increase of H+ ions), and a significant drop of the total hardness (= decrease of Ca/Mg ions). Due to the big amount of H+ ions in the water column, alkalinity (KH) will also decrease, because the available bicarbonates (HCO3-) will try to neutralize some of these new H+ ions, so part of the bicarbonates and part of the H+ ions will react forming H2O + CO2. These above described processes will continue until the substrate will be "saturated" (i.e. all the available cation sites will be occupied by the available cations, and an equilibrium will establish). If during the water change we use hard water (with high content of Ca/Mg cations), the saturation state will be established sooner. If we use soft water, the saturation process will run much slower.

_PS: I would like to thank Manuel Arias for his detailed explanation._


----------



## JButera

thanks again Marcel but I think you've scared everybody away..lol


----------

