When an inert substrate matures... - The Planted Tank Forum
 
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post #1 of 10 (permalink) Old 06-28-2012, 09:30 PM Thread Starter
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When an inert substrate matures...

In my 65 gallon tank, i have 2 inches of gravel topped with about 4 inches of coal/iron slag, recently, the blasting grit has taken on a softer more muddy consistency. I am assuming this is largely fish poop and detritus, stirred in by the cory cats, trumpet snails and goby.


Now, do these organics provide cation exchange at the roots?

The majority of the substrate is deeply rooted, which would lead me to believe it is for the most part aerobic.

From the little available information on slag composition, it looks to be comprised of Mg, calcium, Fe, and a few other micros. I dont think it is dissolving, maybe just being broken down into finer dust by the fish foraging?

Sorry for the inorganized questions, i'm just curious.
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post #2 of 10 (permalink) Old 06-28-2012, 11:14 PM
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Did you look at the MSDS sheet for any one of the blasting sand products? Here is a good breakdown of contents:

http://www.marco.us/select/datasheets/93714.pdf

I would assume that the stuff you are seeing is a combination of mulm and degraded (particle size) slag. I doubt that much is dissolving.

I won't pretend to be an expert on cation; I cannot answer many of your questions.

There was a thread on certain forum for monster fish that discussed blasting sand/slag as a substrate....some guys had concerns about the levels of aluminum oxides and biproducts found in slag and the effect it would have on plants.


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post #3 of 10 (permalink) Old 06-28-2012, 11:15 PM
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Very fine organic matter (called humus) does have some cationic exchange capacity.

I think the softer stuff you are finding in your sand-like substrate is organic matter. (Fish poop, fallen fish food, dead plant parts) that are in the process of being decomposed. Another name for this stuff in the fish tank is mulm.

I do not think your substrate materials (gravel and slag) will break down to smaller particles very easily. The actual elements they are made of (Mg, Ca, Fe etc) are probably so tightly combined with each other that they are not available to the plants as nutrients.
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post #4 of 10 (permalink) Old 06-29-2012, 01:44 AM Thread Starter
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I've seen the msds for one brand, not the stuff I have now. It seems to me, also, that each batch will be different depending on the ore used, temperature of firing, how well it was rinsed before packaging; etc... What i think i have is black blast, came in a clear and white bag with a blue spout.

As far as the plants go, i have never seen finer, more networked root systems. It packs a little, but not so much that plants have trouble. I usually manually aerate the soil when i plant anyway.

Maybe some day i will conduct a controlled test.

One thing i do worry about though, is the substrate's ph dipping, with all the organics in it... Only time will tell.. any info from long time user would be great, too!
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post #5 of 10 (permalink) Old 06-29-2012, 07:17 AM
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Cation exchange capacity is the ability of the medium to attract positive charged ions called cations and hold them. Cations are the chemical molecule of various minerals and other nutrients. The medium must be porous and have a negative chemical charge that attracts the positive charged cations. In simple terms it holds the nutrients like a sponge so that when it comes into contact with plant roots, the roots can absorb these nutrients.

"Organics" do not lower the pH. Organic acids do. Minerals, slag, gravels are not organic. Organics are vegetable, plant, and feces matter. Some organic matter such as peat and humus have CEC. Some media attracts negative ions which are called Anions. Some media retains small quantities of anions, negatively charged ions, in addition to cations. However, anion exchange capacities are usually negligible, allowing anions such as nitrate (NO3-), chloride (Cl-), sulphate (SO4-), and phosphate (H2PO4-) to leach from the media.

Important cations in the cation exchange complex in order of adsorption strength include calcium (Ca2+) > magnesium (Mg2+) > potassium (K+) > ammonium (NH4+), and sodium (Na+). Micronutrients which also are adsorbed to media particles include iron (Fe2+ and Fe3+), manganese (Mn2+), zinc (Zn2+), and copper (Cu2+).

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post #6 of 10 (permalink) Old 06-29-2012, 08:01 AM
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In general organic matter have a high CEC. Even higher than most clays, especially baked/fired clay as the clay lose some CEC in that process.

http://www.dpiw.tas.gov.au/inter.nsf...tsoforganicmat
Quote:
Table 3. Cation exchange capacity of different soil particles

Soil particle

CEC (cmol/kg)
Humus
100-300
Smectites (black swelling clays)
60-150
Kaolinite (white potterís clay)
2-15
Iron and aluminium oxides (from ferrosols)
<1
Source: McLaren and Cameron (1996).

Please ignore any spelling/grammatical errors. I'm swedish and sometimes I'm also drunk.
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post #7 of 10 (permalink) Old 06-29-2012, 11:01 AM Thread Starter
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So, basically, fish poop really is the best thing plants?
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post #8 of 10 (permalink) Old 06-29-2012, 01:16 PM
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I think a blend is best of all.
No one material is 'The Best'.
Each offers different things.

Sand/silt/clay offers secure rooting media. A place for roots to hang onto and support the plant. A place for all the microorganisms to hang onto. The clay fraction does offer the CEC, at whatever level.

Fish poop, fallen food, leaves, dead roots and so on are constantly decomposing and more debris falling. This activity supports a LOT of microorganisms and is part of the whole ecosystem, but is not the only part of it.
Once these organic materials are broken down so they are just a few molecules in size they can then act as cationic exchange sites, or are broken down to the point that they are fertilizer (including carbon) for the plants. A chunk of leaf or a stick from your compost pile is too big to be active like humus is.
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post #9 of 10 (permalink) Old 06-29-2012, 03:05 PM
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Quote:
Originally Posted by Diana View Post
Once these organic materials are broken down so they are just a few molecules in size they can then act as cationic exchange sites, or are broken down to the point that they are fertilizer (including carbon) for the plants. A chunk of leaf or a stick from your compost pile is too big to be active like humus is.
Porous/fibrous/spongy organic material like peat/humus have a high CEC even when in larger chunks(a lot bigger than a few molecules), as they have big surface on the inside.

For example look at this picture.
http://www.johomaps.com/na/canada/bc...peat/main.html

Mineral material have to be really small(<2Ķm) as it's only the outside that have a surface.

Please ignore any spelling/grammatical errors. I'm swedish and sometimes I'm also drunk.
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post #10 of 10 (permalink) Old 07-01-2012, 03:03 AM Thread Starter
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Thank you guys.
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