Clay in Topsoil - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 01-06-2012, 08:46 PM Thread Starter
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Clay in Topsoil

do i need to add pottery clay to the topsoil to bind the particles together and keep it from clouding my water?

also do i need to rinse coal slag before i use it as a cap?
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post #2 of 8 (permalink) Old 01-06-2012, 09:06 PM
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Originally Posted by calebjimz View Post
do i need to add pottery clay to the topsoil to bind the particles together and keep it from clouding my water?

also do i need to rinse coal slag before i use it as a cap?
The reason most people use some clay is for the iron content, but if your making some MTS I suppose it could do a nice of bonding as well. You don't need to do it. I have a tank with and one without, really no difference...other than one might have more iron available to the roots of the plants.

Your water will likely cloud a little regardless. It will do this with or without the clay in my opinion...but it's nothing that shouldn't be gone in 24 hours.

I haven't needed to rinse any of my coal slag. That said, it is a raw industrial product...your mileage may vary.
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post #3 of 8 (permalink) Old 01-06-2012, 11:03 PM
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The clay will offer no binding properties. It is used for the nutrients in it.
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post #4 of 8 (permalink) Old 01-07-2012, 05:26 AM
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The clay will offer no binding properties. It is used for the nutrients in it.
I think clays are naturally high CEC materials too, so they might be improving the MTS by raising its CEC. A lot of real topsoil contains some clay naturally, so you can't really generalize about adding clay to real topsoil substrates. Bagged stuff called topsoil probably doesn't have any clay in it.

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post #5 of 8 (permalink) Old 01-07-2012, 07:30 AM
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http://www.thekrib.com/Plants/Fertilizer/laterama.html

"Substrates with CEC help plants to capture and absorb important nutrients
with their roots. Plant roots secrete organic, humic acids (found in
humus) which are able to displace the nutrient cations, bind them
into soluble chelates and make them available for absorption into
the root where they are transported to the leaves for use by the plant."

the important of organic materials in substrate


"Laterite is comprised of Fe and Al oxides and kaolinite-like clays
which contribute little to the CEC of the substrate. Jim mentions other
amorphous minerals of volcanic origin (presumed in laterite) which
have high CEC and may contribute to laterite's CEC. In addition,
the hydrous oxides of Fe & Al in laterite can have anion exchange
sites which may be important for phosphate ions. Jim didn't talk much
about anion exchange or how important it is relatively. He did talk
about the possible benefit of iron oxides in reducing phosphate
concentration by attracting these anions and making them chemically
unavailable. The iron oxide needn't be in laterite to perform this
function but should be in the substrate if there is some degree of
substrate circulation."




Weather or not Iron i leach into the water column is debatable, but here is my theory

Latterite clay (and related clays) contain numerous type of iron oxide although usually insoluble, it can be made to free ions by naturaly occuring oxalic acid (Or other chelating acids) in mature tank.

Example

Fe2O3 (solid) + 3H2C2O4(aq) -> Fe2(C2O4)3(slightly aq) + 3H2O


Hope that help
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post #6 of 8 (permalink) Old 01-07-2012, 01:51 PM
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That would be a Cool sig line

"Fe2O3 (solid) + 3H2C2O4(aq) -> Fe2(C2O4)3(slightly aq) + 3H2O"
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post #7 of 8 (permalink) Old 01-12-2012, 10:25 AM
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Quote:
"Laterite is comprised of Fe and Al oxides and kaolinite-like clays
which contribute little to the CEC of the substrate. Jim mentions other
amorphous minerals of volcanic origin (presumed in laterite) which
have high CEC and may contribute to laterite's CEC. In addition,
the hydrous oxides of Fe & Al in laterite can have anion exchange
sites which may be important for phosphate ions. Jim didn't talk much
about anion exchange or how important it is relatively. He did talk
about the possible benefit of iron oxides in reducing phosphate
concentration by attracting these anions and making them chemically
unavailable. The iron oxide needn't be in laterite to perform this
function but should be in the substrate if there is some degree of
substrate circulation."
That brings back memories. That's a quote from a list serv in 1995 to 1999, and I was part of those conversations.

Clay and laterite are high in oxidized minerals, mostly iron. Oxidized iron is Fe+3. In order for plants to use minerals they need to become water soluble, and this is done by organic acids or chelators. The chelator changes the Fe+3 iron cation to Fe+2. There are a number of different acids that can do this. In a mature tank, (as in YEARS, not six months) this can happen from the humic acids of fish waste, plant mass, fish food. Peat, soil, and other rotting organic material will also provide the acids for this process.

Cation exchange capacity is the ability of a medium to attract positive ions like Fe, bind them and hold them for plant uptake...like a sponge. Fired clay is very high in CEC. Raw clay is not. Laterite is actually even lower in CEC than raw clay.

Jamie Johnson did a soil analysis and CEC analysys on several substrates, clays and laterites you can see the results
HERE

The reason for using clay or laterite has always been to supply a continual source of oxidized iron which works in conjuction with organic acids.

Robert Paul Hudson

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post #8 of 8 (permalink) Old 01-12-2012, 11:15 AM
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Quote:
Originally Posted by Robert H View Post
That brings back memories. That's a quote from a list serv in 1995 to 1999, and I was part of those conversations.

Clay and laterite are high in oxidized minerals, mostly iron. Oxidized iron is Fe+3. In order for plants to use minerals they need to become water soluble, and this is done by organic acids or chelators. The chelator changes the Fe+3 iron cation to Fe+2. There are a number of different acids that can do this. In a mature tank, (as in YEARS, not six months) this can happen from the humic acids of fish waste, plant mass, fish food. Peat, soil, and other rotting organic material will also provide the acids for this process.

Cation exchange capacity is the ability of a medium to attract positive ions like Fe, bind them and hold them for plant uptake...like a sponge. Fired clay is very high in CEC. Raw clay is not. Laterite is actually even lower in CEC than raw clay.

Jamie Johnson did a soil analysis and CEC analysys on several substrates, clays and laterites you can see the results
HERE

The reason for using clay or laterite has always been to supply a continual source of oxidized iron which works in conjuction with organic acids.
Hi robert, i use potting soil as the bottom layer which i believe will release organic acid. But one of my main concern is that it might release Ca and Mg ions also.. any information on that?
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