# What is a CEC rating?



## Guyver (Feb 12, 2010)

I hear the acronym around here, but don't know what it means? Anybody care to inform me? Thanks.


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## klaus07 (Nov 23, 2011)

cation exchange capacity. It refers to the ability of a substrate to make available to the roots of plants those micronutrients plants need for life and good growth. For example Iron. Not all iron is the same, for example simply putting a rusty nail in your aquarium won't do the trick. The iron must be in a soluble form that can be loosely held by the substrate so the plant can use it.


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## Guyver (Feb 12, 2010)

So is the CEC rating independent of the mineral concentrations in the soil? For example, can you have substrate with a good CEC but not a high concentration of the soluble iron?


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## m8e (Oct 16, 2009)

Yes. For example active carbon has a really high CEC value, but it is pretty much empty.

The CEC rating is kinda like the mAh rating of rechargable batteries. A 1.2v x 2400mAh cell can hold double the charge(energy) compared to a 1.2v x 1200mAh cell, but both are pretty much empty when you buy them. But some batteries (and substrates) is precharged.


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## klaus07 (Nov 23, 2011)

Think of the substrate as velcro. The Cations stick to the "velcro" until the plants pull them off the velcro and absorb them through their roots. If the nutrient is not in the correct ionic state it won't stick to the substrate and the plant cannot absorb it.


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## Guyver (Feb 12, 2010)

Great info guys, thanks for sharing. Where can I find things like the CEC rating and mineral content of substrates?


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## diwu13 (Sep 20, 2011)

There's not a real "rating" for CEC but some substrates are classified as "high CEC" and others have "none". There's really nothing inbetween that I know of.

Here's a general list that's a quick read: http://www.plantedtank.net/forums/substrate/153412-substrate-choices-pros-cons.html
but for a more thorough breakdown of nutrients you'll need to go to each of the substrates home pages.


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## Diana (Jan 14, 2010)

When you buy a substrate, get high CEC, and do not worry if it comes with added fertilizer. If it does, the fertilizer will just get used up, and you have to add ferts. If there is no fertilizer to get started you have to add ferts. See? either way you add fertilizer. So why pay so much more for 'pre-loaded' substrate?

Material with high CEC include clay and humic particles. 
Clay can be found in some garden soils (and gardeners swear at it), and can be processed into a material like Turface, kitty litter or Oil-Dry sorts of products. When the clay is compacted a special way it still has very high CEC, but will not cloud the tank. The particles act more like a lightweight sand. 
Humic materials are organic matter that has been composted so well it is very fine particles, and you cannot tell what they used to be.


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