Can high CEC substrates be "recharged"? - The Planted Tank Forum
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post #1 of 13 (permalink) Old 02-07-2011, 06:05 AM Thread Starter
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Can high CEC substrates be "recharged"?

non-inert substrates like flourite, ecocomplete, etc....can nutrients be re-sequestered into them, essentially making them viable again? Can nutrients in the water column, decomposing mulm working its way into the substrate, or mineralized organics like processed compost or worm castings eventually work itself into the substrates?

The reason I ask is because it seems to be a common scenario where the substrate is exhausted of its nutrients and the user has to resort to either replacing the substrate or forming a regiment of water column dosing. Isn't the point of getting high CEC substrates is so that it can absorb "excess" nutrients, hold onto it and slowly release when needed?
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post #2 of 13 (permalink) Old 02-07-2011, 12:29 PM
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substrate ferts are the best way to achieve this. Rootmedic root caps work wonders for my tanks b/c all of my substrates are inert.


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post #3 of 13 (permalink) Old 02-07-2011, 03:48 PM
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Flourite and Eco Complete are inert substrates. High CEC just means the particles have large surface areas and are structured so as to attract and hold positive ions like ammonium and potassium so plant roots can access them easily. That capability doesn't wear out or deplete.

The popular nutrient rich substrate is ADA Aquasoil, which contains bioavailable nutrients which are used up by the plants over many months of use. Those can't be replenished, but they can be substituted for with substrate fertilizers. MTS is another nutrient rich substrate, but how rich depends on what topsoil is used to make it. It too can eventually be depleted of some of its nutrients, and those can be substituted for with substrate fertilizers.

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post #4 of 13 (permalink) Old 02-07-2011, 04:06 PM Thread Starter
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I think you just answer my question hoppy. When people said that their substrate was "depleted", I literally thought that it meant that it had become useless, even in its ability to attract cations.

But say your "dosage" of NPK depended on fish poop and the like, and an occasional GH raiser with Potassium. In theory, if there were enough of these nutrients in the water column that weren't being used fast enough by plants, they could become reattached to the deplete substrate. I know for a fact that roottabs and other substrate fertilizers do the job but is that theory somewhat correct?

Also, isn't the point of using soils is for their higher CEC?
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post #5 of 13 (permalink) Old 02-07-2011, 04:36 PM
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Substrate is substrate. You can continue to add new substrate on top of your old substrate.
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post #6 of 13 (permalink) Old 02-08-2011, 03:21 AM
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Substrate is substrate. You can continue to add new substrate on top of your old substrate.
Well, up to the point where gloss can't grow in the last half inch of water.
post #7 of 13 (permalink) Old 02-10-2011, 05:31 AM
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Tom Barr did a great study on ADA aquasoil, where he measured the initial nutrient content vs. a batch that was 18 mo. old. It is indeed possible to replenish Aquasoil with just water column dosing (EI). The study requires a membership to Tom's site, but it's money well spent. I don't want to give too much away, since he put a lot of time and money into performing the study, but it is a fascinating read.
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post #8 of 13 (permalink) Old 02-10-2011, 01:21 PM Thread Starter
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Thanks for the info, I'll try to check it out.

I used to do alot of container gardening and I'm not sure how much of that hobby can be translated to the aquarium hobby, but the main issue of container mediums wasn't necessarily replenishing the nutrients but picking a medium that doesn't degrade and therefore compact with time and choke off supply of nutrients and oxygen and restricting root growth. If the same rules apply, assuming you start off with a high CEC inorganic substrate, it could potentially sequester nutrients indefinitely.
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post #9 of 13 (permalink) Old 02-11-2011, 03:22 AM
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Land and container gardening has a lot in common with aquatic gardening, but there are some important differences.

Land plants are not especially noted as being capable of adding oxygen to the soil.
Aquatic plants do this a lot.

The natural soil that aquatic plants grow in (a lake, for example) is already compacted, anaerobic goo. We do want something a bit better in our tanks, because we are also keeping fish, and the anaerobic substrate creates conditions that can kill fish.

The natural soil that land plants live is is usually not compacted, and their roots are not capable of handling those conditions (poor air and water movement and related issues).

In containers you are watering a lot, because they dry out a lot. This is like forced aging, or mineralizing the soil. Every few years it is common to unpot the plants, scrape off any loose soil and repot using as much new soil as possible. This is supposed to replenish whatever has happened to the old soil because of this forced aging.

This does not happen so much in aquariums. A good substrate should not break down in an aquarium.
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Soil, for land plants or aquariums is most basically a mineral component, and an organic matter component.
The mineral component is a combination of particle sizes called sand, silt and clay. There may be larger particles, gravel, pebbles, rocks... call it what you want. Not soil particles.
The organic fraction is dead matter from plants and animals, in various stages of decomposition. Fallen leaves, manure, grass clippings and all sorts of other things.
For our gardens many of us make a compost pile and break down organic matter that way.
In nature composting takes time, and organic matter in soils can be in many particle sizes. The smaller particles interact with the smallest mineral particles (clay) and the clay soils become better textured when there is plenty of organic matter blended with them.
As the organic matter in our garden soils and containers breaks down you have to keep adding more. Mulch, compost...

In an aquarium, or in a lake there is a constant rain of organic matter. Fish food, falling leaves, fish poop, dead bugs...
Decomposition happens under water, too, but perhaps at a different rate than on the land. The microorganisms that break down organic matter work better with more oxygen. Higher oxygen levels on land, at the surface of the soil (think fallen leaves on the forest floor) allow the material to decompose very fast. So there is a constant trickle of decomposing organic matter carried into the soil by worms, gophers and other animals.
In an aquarium or lake there is less oxygen in the substrate. The decomposers work slower. Unless you have MTS or other diggers the organic matter is not constantly getting blended with the lower levels of substrate. In many aquariums (non-planted especially) this is getting vacuumed out frequently.
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In an aquarium, too much organic matter is generally not good. As it breaks down there is ammonia and CO2 added to the water. Sounds great for plants, but this can be overdone.
A more mineral based substrate is better in an aquarium. Clay sized particles have high CEC no matter if they are clumped together or separated. A baked clay substrate that is handled gently so it does not fall apart is a very good substrate.

Clay soil in the garden can be very good, too, but is hard to work. It must not be compacted, or it loses its great texture. It takes time to add enough organic matter to make a poor clay soil into a good soil. Then you need to keep adding organic matter. Clay particles are especially difficult to work with in containers, so mostly people avoid it by using a sandy loam with lots of compost in containers, or even a soil-less mix of perlite and compost. The organic component still needs to be replaced in these soil-less mixes.
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post #10 of 13 (permalink) Old 02-11-2011, 12:02 PM Thread Starter
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Excellent post Diana! I am an avid gardener, so I love the comparisons.

So what I'm getting is that particle size and organic matter, two things that are key issues in terrestrial gardening, is not so important for planted tanks. I figure since most substrates in planted tanks are going to go anaerobic to a some degree in the long run, more organic matter just equals greater risk of detriment for the fish.

Which leads me to my next question. Are fully matured composts (like 2-3 years old) and vermicomposts (fresh or aged) already mineralized enough so that it will be safe to as a supplement to substrates?
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post #11 of 13 (permalink) Old 02-11-2011, 02:47 PM
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Which leads me to my next question. Are fully matured composts (like 2-3 years old) and vermicomposts (fresh or aged) already mineralized enough so that it will be safe to as a supplement to substrates?
This doesn't exactly answer your question, but I would put them through a few wet/dry cycles to be sure.





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post #12 of 13 (permalink) Old 02-11-2011, 10:08 PM
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Originally Posted by Indignation View Post
Tom Barr did a great study on ADA aquasoil, where he measured the initial nutrient content vs. a batch that was 18 mo. old. It is indeed possible to replenish Aquasoil with just water column dosing (EI). The study requires a membership to Tom's site, but it's money well spent. I don't want to give too much away, since he put a lot of time and money into performing the study, but it is a fascinating read.
It required a lot more $$$ and time for me personally

Basically, the ADA AS or any clay loam ought to be relatively close, will decline in Nitrogen over time.

The other ferts will still be there.
I suppose if you did not dose anything to the water, then they will be drained also at a higher rate, but they should last 5-10 years or so for most things except N and dosign K+ and traces will certainly help, as well as PO4.




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post #13 of 13 (permalink) Old 02-12-2011, 11:15 PM
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I would think since its porous, it would get clogged up and unable to hold nutrients as efficiently. So couldnt you boil it to release all the crap thats in it?

Or are you trying to replenish it without tearing up your tank? lol
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