# Rechargeable substrate ?



## old 97 (Jul 25, 2011)

Does my/your substrate act as a battery?
Is it rechargeable?

Can I add a salt to the water column and have it "hide" in the dirt ?
Can ferts disappear into the dirt and  become available to plants? - and can the opposite happen?

Sequestering, bioavailability, chelating agents, - heard of them; and they somehow relate to my curiosity.

Can anyone offer insight or suggest reading material?

Anyone know of an article titled ?
"just because you dumped it in the tank doesn't mean your plants can eat it "
OR
"why putting a paper clip in your tank will/will not supply plants with iron"


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## Sake (Apr 20, 2012)

Some substrates will hold onto ferts and release them when needed, safe t sorb does this. Look up CEC (cation exchange capacity) and it will explain more.


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## Diana K (Dec 20, 2007)

Research using the term Cationic Exchange Capacity. 

Fine soil particles, clay and humus are so small they can become negatively charged in nature. That is, the particle tends to have slightly more electrons on its surface. 
This is just enough that molecules of fertilizer that are charged (anions and cations) are attracted to the soil, and will cling, just a bit. The positive molecules cling closer to the soil, then the negative molecules are attracted to that. Humus can have either a positive or negative charge. 

Plants can make use of this. They release charged atoms such as hydrogen (H+) and potassium (K+) into the soil through their roots, and this disrupts the soil-fertilizer bond, and the plants can take in the fertilizer. 

This only works when the fertilizer is in very small molecules, or single atoms. Larger molecules, such as chelated minerals are available to plants via another mechanism. 

Soils with high CEC include most of the ADA products, and montmorillonite clays such as Safe-T-Sorb. 
As organic matter (fallen leaves, dead roots) decompose it becomes so fine that it also acts like this. 

Cationic Exchange Capacity works the same in your garden soil. Clay soil, while it can be difficult to work, can also be very rich in fertilizer. Adding compost to the soil every season is also adding to the CEC of the soil as it breaks down.


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## Zapins (Jul 28, 2004)

Oh boy. Lots of good questions.



old 97 said:


> Does my/your substrate act as a battery?
> Is it rechargeable?


Rechargeable? Not in that sense of the word no. Nutrients can be stored in the substrate and released slowly over time, but once they are gone they are gone and cannot be replaced while in the tank. You can always add root tabs and that sort of thing to replace some of the ferts that have been used up but you can't really dose chemicals into the water column and have them become concentrated in the soil.



old 97 said:


> Can I add a salt to the water column and have it "hide" in the dirt ?


Yes, some soils will absorb sodium because it is positively charged and it will be attracted to the negatively charged substrates. Clay is negatively charged so any soil that has clay or other negatively charged particles will attract sodium and cause it to "hide" out in the substrate.



old 97 said:


> Can ferts disappear into the dirt and  become available to plants? - and can the opposite happen?


Yes they can, to some extent. Mostly the positive ions are sequestered by certain substrates. This is due to charge attraction between the + of the ion and the - of the substrate. There is a limit to how much a substrate can absorb though. At some point enough + ions enter the soil and reduce the - charge of the soil on other ions. So this effect isn't an infinite sponge. At some point it will balance out more or less. These ions in the soil may or may not be available to the plant. Some of them react and become unusable to plants. Aquatic plants absorb nutrients from their leaves, stems and roots so anything dissolved in the water column will be available to the plant it doesn't have to be absorbed through the roots to be available.

Another interesting point to be aware of is that if your soil has a lot of nutrients in it all bound up with clay you can encourage these nutrients to be released into the water column and root zone by adding certain minerals to the water. Basically this works because some ions, like calcium, want to be with the negatively charged clay particles more than other ions do. So if those ions are bound up in the clay, the calcium will muscle its way in there, hog all the negative charge and the other ions will no longer be attracted and bound up in the clay. This increases their availability to plants. This is probably why dosing potassium is recommended when using aquasoil after the first few weeks. The constant addition of potassium muscles its way into the clay and releases other nutrients stored there.



old 97 said:


> Sequestering, bioavailability, chelating agents, - heard of them; and they somehow relate to my curiosity.


Your previous question leads into this one really well. Basically nutrients are absorbed by plants in certain forms and if those forms are not available to the plant then the nutrients do not get absorbed. This is more a problem with trace elements than with macros since trace elements are quite a bit more chemically reactive and unstable than macro nutrients. So things like iron are absorbed in Fe+2 form not really Fe+3 form (rust). This is where chelating agents like EDTA come in, they force (sequester) the iron to remain in the Fe+2 form and therefore make it more available to the plants by prolonging the time Fe+2 hangs around in the water column (bioavailability). The story is similar for the other micros.



old 97 said:


> Anyone know of an article titled ?


"just because you dumped it in the tank doesn't mean your plants can eat it "
OR
"why putting a paper clip in your tank will/will not supply plants with iron"[/QUOTE]

Never heard of them before, but if you have the link to either of them I'd love to read them.

The paperclip title sounds like it is explaining the difference between Fe+2 and Fe+3 (rust isn't usable by aquatic plants).


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## Diana K (Dec 20, 2007)

One of my horticulture teachers had a picture of a plant with its roots wrapped around a hamburger, and the plant was showing all the nutrient deficiencies. 

His point was exactly the same as the 'articles':
A hamburger represented all the nutrients that plants need, but bound up in ways the plants could not use them.


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## Zapins (Jul 28, 2004)

Diana K said:


> One of my horticulture teachers had a picture of a plant with its roots wrapped around a hamburger, and the plant was showing all the nutrient deficiencies.


Reminds me of the state of our diet nower days :-/


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## niko (Jan 28, 2004)

Why on Earth do we have to have such discussions when all you can do is add enough of all fertilizers in the water and change 50% water once a week? How many more people need to show beautiful, clean, stable tanks that are run that way?


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## Cavan Allen (Jul 22, 2004)

niko said:


> Why on Earth do we have to have such discussions when all you can do is add enough of all fertilizers in the water and change 50% water once a week? How many more people need to show beautiful, clean, stable tanks that are run that way?


Really man? Is the sarcasm really necessary? Again?

BTW, I do pretty much what you described and my tank is pretty stable and clean, though not many would call a farm beautiful. Anyway, there are different ways to supply plants with what they need, and I'm sure you agree that good filtration, a clean water surface, sufficient co2 and a few other things can be common to all of them.


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## Sake (Apr 20, 2012)

niko said:


> Why on Earth do we have to have such discussions when all you can do is add enough of all fertilizers in the water and change 50% water once a week? How many more people need to show beautiful, clean, stable tanks that are run that way?


Have you ever gotten really busy with work or whatnot, working 20-16 hours a day for a few weeks? That's why we have these discussions.


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