# An Opinion about Aeration and CO2 Offgassing in the Low-tech Planted Tank



## Django (Jun 13, 2012)

This opinion has been formed from reading posts and from experience with my aquarium for most of the past three years. My tank is well-planted and has never had an airstone in it. Now, I have an internal filter which, while it does create some minor surface wavelets where the water flow hits the opposite wall, creates no air bubbles.

An integral introductory question about aeration is, "Does aeration add oxygen to the water?" I conclude that the answer is "No." The surface agitation and the upward water movement of the airstone allow for more gas exchange of oxygen at the water surface, increasing dissolved oxygen under normal conditions as we would like, as during proper water movement in the tank, but the oxygen in the air bubbles themselves at the surface of the bubbles exchanges very little in the second before it hits the water surface (source: post).

What aeration/injected air does is raise the gas pressure of the water, forcing gases to come out of solution in the same way water boils in a teapot, and actually reducing the total amount of dissolved carbon dioxide, a nutrient for plant growth. Higher dissolved gas pressure will push gases out of solution, escaping through the water surface interface.

We have so little carbon dioxide in our low-tech planted aquaria to feed our plants, as little as 3 parts per million, that I would like to conserve what we have for use by the plants. I know that in addition to atmospheric carbon dioxide, everything in the aquarium that respires produces carbon dioxide, which increases overnight. To my mind, and I know this comes directly from posts, we should attempt to save the carbon dioxide to feed the photosynthesis of the following day.


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## roadmaster (Nov 5, 2009)

I recall a thread on an ancient forum "the Krib" where this topic was discussed at some length (does aeration increase oxygen).
Dissolved O2 meter suggested that it does increase O2 even at deeper levels in the tanks where it was measured with air stones and without at differing depth's.
I believe current consensus among many is that a good surface rippling helps bring CO2 to the tank from atmosphere above the surface.
I have tried both limiting surface disruption,and creating same over the last three year's.
Can't say I have noticed much difference in my low tech affairs, but I have two Spray bars just below the surface creating rippling as well as a power head pointed straight up to create more rippling and plant's as well as fishes still manage to thrive.


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## Django (Jun 13, 2012)

Yeah, I haven't noticed much difference from when I was running an AquaClear 30 and now, but I noticed a big difference when I put in the soil substrate and also when I started 1/4 EI.

I half-disagree with the idea of surface agitation bringing in CO2. I could think about surface gas exchange like a 1/2" tube with water running through it, in zero gravity. We'll blow on the end that has more water, and the water will go the other way. I think this is analagous to the behavior of dissolved gases in Dalton's Law of Partial Pressures, at least part of it - it's very comprehensive. Not having read it myself, I think that the atmosperic pressure and dissolved partial pressure of the gas work like an equilibrium reaction, and if both pressures are equal, nothing happens, no movement.

Thanks for the info on O2. I was meaning that the actual O2 gas in the bubbles did not contribute much, and actually the dissolved gas pressure increase by aeration injection might offset it.


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## Raymond S. (Dec 29, 2012)

Since I have not studied it "in depth" as far as gas exchange rate of various substances such as O2 and CO2 is concerned I don't know if those rates are identical or not.
I consider this statement to be an opinion, but do not contend the idea that it is noticeably less O2 gleaned it than that which is exchanged from the extra water being in contact/w the surface than before it was circulated by the rising air bubbles.
"but the oxygen in the air bubbles themselves at the surface of the bubbles exchanges very little in the second before it hits the water surface (source: post)."
As is described in this statement...
" upward water movement of the airstone allow for more gas exchange of oxygen at the water surface, increasing dissolved oxygen under normal conditions"
But I'd also like to point out that CO2 also exchanges FROM the air INTO the water
when it is higher in the air than that level which is in the water at this same time.
Though it likely will be still labeled as opinion, all tank owners who use an air stone say they see a noticeable difference in the level of a healthy tank overall AS the result of adding the air stone to it.

I would appreciate it if any low tech tank owners who have noticed that the health of their tank went down when aeration was added to their tank to reply to this post.
It would help to add credibility to either side of this interesting issue.
Because when I'm forming a theory, I should consider all evidence which is available and not only that which supports my theory. So I'd like to hear from any of those who noticed the tank health going down as the result of adding aeration as well.


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## Django (Jun 13, 2012)

Raymond, I don't think you can form your theory on qualitative observations. I personally think the answer can be found in Dalton's Laws re: dissolved gases/partial pressure. Unforrtunately I have not really delved into it yet.


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## roadmaster (Nov 5, 2009)

We know fishes need/use oxygen.
Ditto for nitrifying bacteria.
If little oxygen can be obtained through aeration/air stones, then I should think fishes in grow out tanks or breeder tanks with no filtration other than an air driven sponge filter would be under near constant stress due to low oxygen content?
Nitrifying bacteria would not be able to function very efficiently?
I raised a group of 7 Discus in a 55 gallon (no plant's) with temp of 84 degree's F (less oxygen at warmer temps) with nothing but two Hydro V sponge filter's powered by a luft air pump and air stones for nearly six month's.
I should think the fishes would not have survived long at these temps if low O2 was an issue.


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## Django (Jun 13, 2012)

You make a good point. But a main point I am trying to make is that you don't need air bubbles to make oxygen. I know this is getting old fast but you can oxygnate a tank with the proper water flow, which is like a steamroller or cylindrical shape going from the filter output (I'm excluding foam filters for the moment) in a circle back to the input.

I would never advocate a system which isn't well-enough oxygenated for the fish to stay happy - I would advise anyone to put in an airstone immediately if they have reason to believe there isn't enough oxygen in the water. I believe the water movement and surface agitation of an airstone can help a filter with getting oxygen into the water, especially when the proper water movement is not already present The proper water movement gets the de-oxygenated water in the lower half of the tank up to the surface where it can take up oxygen ad. infinitum.

There is a guy who lives on an island near the shore and runs small reef tanks with one airstone. From Julian Sprung, I think.


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## roadmaster (Nov 5, 2009)

Agreed.
I also like to add a small air stone in holding bucket during drip acclimation as well as a few drops of Prime.


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## Django (Jun 13, 2012)

New CO2 data. Ref. [http://www.newton.dep.anl.gov/askasci/chem03/chem03761.htm].


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## Raymond S. (Dec 29, 2012)

Django said:


> You make a good point. But a main point I am trying to make is that you don't need air bubbles to make oxygen. I know this is getting old fast but you can oxygnate a tank with the proper water flow, which is like a steamroller or cylindrical shape going from the filter output (I'm excluding foam filters for the moment) in a circle back to the input.
> 
> I would never advocate a system which isn't well-enough oxygenated for the fish to stay happy - I would advise anyone to put in an airstone immediately if they have reason to believe there isn't enough oxygen in the water. I believe the water movement and surface agitation of an airstone can help a filter with getting oxygen into the water, especially when the proper water movement is not already present The proper water movement gets the de-oxygenated water in the lower half of the tank up to the surface where it can take up oxygen ad. infinitum.
> 
> There is a guy who lives on an island near the shore and runs small reef tanks with one airstone. From Julian Sprung, I think.


Would that you had stated this in the beginning, it would have removed my feeling that you were giving a one sided notion to newer people.
But then could have/should have etc.....
Take for example, the most commonly talked about subject in American 
small talk sessions...football. Everyone's an expert if you listen to them.
But since I lean heavily on personal experience over numbers on a paper,
the fact that none of them has played professional football, coached a professional football team, managed or owned a professional football team
then I say the none of them are qualified to even talk on the subject.
Watch the static over that remark...LOL...
But hundreds of tank owners who say their tank is better since they added aeration qualifies as more weight than some numbers on a paper somewhere...to me...
This was my reason for bring up what I did.
Not for sure as any kind of challenge to anything you have stated in the quote above as it sheds far more light on what you were getting at.
My apologies if it seemed that way to you.


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## Django (Jun 13, 2012)

I have to apologize for the quick shot I unintentionally zapped you with in reply to your post. I did not intend any static or overtones associated with the statement It was a truly unhelpful post on my part.

Keeping aquaria is such an inexact, subjective hobby. Any other way would be to turn it into a science. I learned through experience and advice with my tank and I really needed to get a feel for keeping the tank and how to react to problems. I remember very well the filamentous algae outbreaks of the beginning time. So I developed a model and add to it ongoingly, but in the meantime, I have something of a feel of things. The most basic thing is what works for me, and maybe I also don't want to rock the boat if it's moving in the right direction.

I'm going to backpedal a little from my last post, which, however, still stands. The biggest thing I have gleaned from this thread is that it is the proper water movement in conjunction with the gas exchange at the surface that bring oxygen into the tank. That's why I like low tanks, because there's proportionally more surface area for gas exchange. That's a big feature of powered filters, and if you're turning over the tank water enough (too much is not necessary) chances are you're moving the water the right way for oxygenation of the whole tank. But I can remember as a kid growing up (dating myself) the old corner filter with carbon and filter floss. And it worked.

Sorry for rambling. And I sincerely apologize for that one-liner.


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## Raymond S. (Dec 29, 2012)

I use DIY low current filters because of a couple of reasons and now have even more reason as Elassomas don't live in any water which has any noticeable current in it.
Backwater fish only so I try to duplicate that for them.
But the second generation DIY filter took water from the bottom of the tank for the intake and discharged it at the top. The first had both intake and discharge at the top but did angle the current up by virtue of using air to run it so that brought the current up and back down to the bottom.
But for that learning part...a few months back I removed all the faster growing plants in there and boy what a mess followed. Took me a few months to figure why and it's just coming back from that now.
When I first did tanks Amazon swords/anacharis and floating hortworth were about the only plants plus vals so starting up four years ago again after stopping in the early 70's
it's a big whole new world in these tanks now. Don't actually want any high tech.
But this Slow tech...well sometimes it is a challenge, to be nice about it...LOL...
About to do the third generation DIY filter/DIY rock background also. We'll see...


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