# Cec & aec



## Flear (Oct 5, 2012)

Cation exchange capacity & Anion Exchange capacity

a high CEC promotes nutrient retention in soils, and i'm assuming the same is true in aquarium substrates (of value for planted tanks)

some nutrients are not retained in such soils due to their inherent negative charges
(sulphate, phosphates, nitrates)

AEC have a tendency to attract these 

while i'm reading up on it now, i'm curious if others have information and/or experience on the subject of using minerals with either high CEC and/or AEC

although i'm finding that minerals that exhibit AEC primarily only exhibit AEC in highly acidic conditions, ... except for oxides it seems.

rings me to two questions.
mixing a high CEC mineral into the substrate with adding AEC minerals/oxides, ... would the substrate retain both positive & negative nutrients ?, would they cancel each other out (bind with each other) and be neutralized ?

and

in the case of oxides, ... (still looking for various types) would that be particularly safe ?


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## Flear (Oct 5, 2012)

is this right ?

redox/ORP 
PH
CEC/AEC

high Redox, relates to low PH, relates to AEC soils
low Redox, relates to high PH, relates to CEC soils
-not to take these as absolutes, but a generalization (may only be right 1/3 of the time. even if correct 1/3 of the time, this is higher than completely random & unrelated all the time)


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## rickey (Jul 7, 2013)

As acidity increases (pH decreases), more H+ ions are attached to the colloids and push other cations from the colloids and into the solution (CEC decreases).AEC generally will increase when pH drops and decrease when pH rises.
Nernst equation relates pH and E-h
What CEC actually measures is the soil's ability to hold cations(positively charged elements) by electrical attraction. The five most abundant exchangeable cations in the soil are calcium (Ca++ ), magnesium (Mg++), potassium (K+), sodium (Na+) and aluminium (Al+++).
R


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