# El Natural and CO2



## Z1234 (Oct 25, 2016)

I am a Hungarian aquarium hobbyist and new to this forum. I always find some new, interesting information in the "Ecology of the PLANTED Aquarium" book every time I pick it up.

I found one scientific article that discusses CO2 root uptake directly from sediment by aquatic plants.

Details here:

http://aob.oxfordjournals.org/content/103/7/1015.full.pdf

Use of sediment CO2 by submersed rooted plants

Anders Winkel and Jens Borum* Freshwater Biological Laboratory, Biological Institute, University of Copenhagen, Helsingørsgade 51, DK-3400-Hillerød, Denmark. Received: 25 November 2008 Returned for revision: 15 December 2008 Accepted: 12 January 2009 Published electronically: 14 February 2009

I have the 3rd revision of the aforementioned book, and I don't recall that this aspect is discussed there.

Would this influence how we set up an El Natural tank? Do I get it right, that in this context sediment mineralization might be counter-productive (in a non-CO2 enriched tank)?


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## Michael (Jul 20, 2010)

Welcome to APC, you have an interesting point! Since most of the substrate CO2 comes from aerobic decomposition of organic matter, organic matter content is an important factor.

I think it comes down to a question of balance, like so many other things in the hobby. You want enough organic matter in the substrate to supply CO2 (at least when the tank is new), but not so much that decomposition switches to anaerobic processes that produce toxic compounds. In my experience, many beginners start with percentage of organic content too high, with the subsequent problems of a mostly anaerobic substrate.

The initial production of CO2 in a properly set up Walstad tank is one of the reasons that plant growth is so fast at first, then slows as the tank matures. Maybe a way to increase growth in a mature tank would be to add organic matter to the substrate in controlled amounts.


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## Z1234 (Oct 25, 2016)

Michael said:


> The initial production of CO2 in a properly set up Walstad tank is one of the reasons that plant growth is so fast at first, then slows as the tank matures. Maybe a way to increase growth in a mature tank would be to add organic matter to the substrate in controlled amounts.


I am guessing that we over estimate the risk of anaerobic conditions and H2S production. Yes, it is a disaster when that happens, especially at new tanks.

However, if plants are established and there are enough roots, maybe the CO2 limitation becomes more of a problem in the long run to maintain large mount of healthy plant mass. Could it make sense to add C somehow to the tank? In the nature, tree leaves and all kind of stuff lands in the lakes.

I am guessing that material with high C:N ratio could work. For example wood chips, dry leaves etc.

I have a tank out in the garden with direct sunlight. What I noticed, especially in the first 1-3 months that when the sunlight hits the aquarium, it bubbles like crazy from the substrate. It is not H2S. It does not smell at all.

However, with newly established aquariums inside the house and artificial light, I still get some bubbles in the beginning, but nowhere close to the sunlight-tank. Somehow for me it appears that sunlight makes a difference.

Maybe with the outdoor aquarium it would make sense to use a tighter cap to "seal" some CO2 in the substrate and prevent that it gasses off so quickly? Or this would be useless / risky?

The study I linked above states that they found that 3 aquatic plants (out of 5 investigated) took more than 75%(!) their C need directly from the substrate. Only one was not able to use substrate-CO2 at all.

This is the garden - sunlight aquarium when it was 3 months old.










It is definitely not an award winning aquascape, but at least plants have been growing healthy. The top is normally open, I only put the cover on to take the picture.


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## micheljq (Mar 25, 2013)

There must be a way to place the soil in a container or something that you can remove when the soil is depleted. Then add new soil in the container, like a mesh bag or something like that.

I was even thinking of putting it in the canister filter but i think it would be ugly or messy or could stop the canister from working. Maybe with a coarse and a fine filter sponge on the top in the canister. Crazy ideas like that..

I continue thinking on this..

Michel.


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## BruceF (Aug 5, 2011)

All of this is so terribly complicated. I have a 10g tank that has had sagittaria growing in it for over four years in the same substrate I first planted it with which was dirt from the yard. It has never had a filter or any water flow. It did used to have some killifish in it but I removed them. I feed it with a diluted fertilizer occasionally. My real point is that I think all this is plant dependent . The crypt nurii on my desk has been in the same substrate for at least three years. I have found it gets better color when it is stressed a bit and grows tall and more green when it is over fed. I have cut back on the ferts in this tank. Hygophilla is another plant that doesn’t seems to need much help in fact fertilizer seem to cause the leaves to get spots and drop off. I keep small internal filters in those tanks and very few fish. 

Just forget the co2 and get the right plants!


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## Z1234 (Oct 25, 2016)

BruceF said:


> All of this is so terribly complicated. ...
> Just forget the co2 and get the right plants!


One can find many photos of awesome NPT aquascapes with moderately difficult plants on the net. There are also some examples of CO2 demanding carpeting plants in NPT, however there the challenge _- to my understanding -_ is to keep them together with other more competitive species because of CO2 limitation. I have not tried to keep carpeting plants in a NPT yet.

The 0.5 mg/l CO2 that comes from the air-equilibrium sounds awfully low to me.

_Is there any NPT practices that we can use to "super charge" our tanks with CO2?_

Most CO2 comes from the substrate. Some plants can take it up directly from there (see first comment), some through the water column, some may use HCO3-.

What I am thinking is like having some emersed plants that pump oxygen to the substrate. Having more oxygen there the bacteria could be more efficient producing CO2. The book mentions that a Waterlily brings several liter of air down to the substrate per day. With this, I doubt there is any chance of anaerobic conditions. In the long run, to ensure there is enough organic matter available, we could stick woodchips (?) into the substrate. Woodchips have a high C/N ratio. Maybe this is just a dumb idea.

In a non-NPT Low Tech tank,_ I am guessing_ that the large bio filter is the main source of CO2. Depending on the water used, frequent water changes may also bring in CO2.


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