# Oxygen blocking CO2



## Edward (May 25, 2004)

Oxygen blocking CO2 fixation

Water surface movement and aeration with low to moderate CO2 injection gives some people better results then high CO2 without water aeration. No idea why, but there may be two possible explanations. One is the Henry's Law on Gas equilibrium in liquids and the other is the function of the plant enzyme responsible for CO2 fixation. This enzyme stops performing when Oxygen levels go up. This happens in the middle of a photoperiod when plants are expelling Oxygen to the water column. Simple water aeration frees the extra Oxygen to the atmosphere restoring the enzyme performance. 
Please see the following article by Vivienne Baillie Gerritsen.

_*Most of us take the oxygen we breathe for granted. Yet were it not for the plant kingdom, and a large and slothful enzyme, none of us would be here. Rubisco is the key enzyme which - in the process of photosynthesis - swallows up atmospheric carbon dioxide and deals with it in such a way that oxygen is released into the air. The release of oxygen is really just a side effect. Rubisco has no particular feelings for humans; it just uses the carbon from the carbon dioxide, which it recycles as sugars for its own selfish purposes. In the same way that we breathe in oxygen for life's sake and recycle the waste as CO2.*_

_Rubisco is one of the laziest - if not the laziest - enzyme on earth. Most enzymes can process one thousand molecules per second; Rubisco plods along at a mere three molecules per second&#8230; To bypass such slothfulness, plants synthesize a gross amount of Rubisco, sometimes up to 50% of their total protein content! Which is a perfect illustration of quantity as opposed to quality. As a consequence, Rubisco is probably also the most abundant protein on earth. Scientists estimate that the biosphere boasts about 40 million tons of Rubisco, i.e. the equivalent of almost 8kg per person!_

_Not only is Rubisco sluggish but it is also unselective. Oxygen can easily settle in the active site thus preventing the fixation of carbon dioxide. It is then added to RuDP and a series of energy-consuming reactions occur to mend the wrong. Hence, Rubisco is slothful and inefficient._

_by Vivienne Baillie Gerritsen_
_http://www.expasy.org/spotlight/back_issues/sptlt038.shtml_

Any thoughts?

Thank you
Edward


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## Avalon (Mar 7, 2005)

*Re: Oxygen blocking CO2 ?*

I don't have any scientific information on that, but since going open-top a few years ago, I've taken a different perspective on things. Generally speaking, I like to keep things in motion. One thing that annoyed me were those massive conglomerations of bubbles that gathered at the water's surface. Since adjusting the water flow to provide some ripple across the surface, I've noticed no lack of CO2, and healthier fish, and good plant growth. I don't know if I could go so far as to say the plants are any healthier, but I can certainly say there was no loss in plant growth/performance. All that stuff about how planted tanks shouldn't have surface aeration is hogwash. I actually prefer some surface movement; it simply creates a healthier enviornment.


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## epicfish (Sep 11, 2006)

*Re: Oxygen blocking CO2 ?*



Photorespiration @ Wikipedia said:


> Photorespiration is said to be an evolutionary relic. Photorespiration lowers the efficiency of photosynthesis by removing carbon dioxide molecules from the Calvin Cycle. The early atmosphere in which primitive plants originated contained very little oxygen, so it is hypothesized that the early evolution of Rubisco was not influenced by its lack of discrimination between O2 and carbon dioxide.


http://en.wikipedia.org/wiki/Photorespiration

Interesting...I've never thought about this.


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## jeff5614 (Feb 15, 2006)

*Re: Oxygen blocking CO2 ?*

I agree with Avalon. I have a 42 inch spraybar with quite a bit of surface agitation on an open top tank. CO2 levels are consistent and the plants and fish are always healthy. I think the idea of using gasping to fish to indicate an ideal CO2 level is ridiculous. All things in moderation.


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## defdac (May 10, 2004)

If high oxygen content would make Rubisco stop working, wouldn't the plants stop pearling?


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## Squawkbert (Jan 3, 2007)

We need a way to differentiate high current effects (correlated w/ higher surface agitation) from the effects of lowering O2 conc.

Any takers?


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## Edward (May 25, 2004)

defdac said:


> If high oxygen content would make Rubisco stop working, wouldn't the plants stop pearling?


Rubisco doesn't stop like a switch, it slows down. And what is also bad is plants grown at high CO2 don't have as much of Rubisko. This makes sence because less of this enzyme is needed to do the job. If CO2 levels drop these plants are in trouble and algae have a better chance. On the other hand plants grown at moderate CO2 levels develop more Rubisco making them more resistant to variations and algae infestation. 

Pearling? What does pearling indicate in terms of plant health? Nothing. 

This is one of the best pearling explanations by HeyPK: 
_Pearling occurs when most of the water is not saturated with O2 because, while a thin layer of water very close to the plant may be saturated, the water further away is not saturated. If the water is not moving in the tank, you will have more pearling than when it is moving, because moving the water clears away or makes thinner the boundary layer of saturated water next to the plant, and, therefore, more oxygen diffuses into the water and less comes out as bubbles. When a plant is pearling, the bubbles come through water that is not saturated with O2, and the gas distribution in the bubble becomes like the gas distribution in the water the bubble is rising through. Basically, even if it comes out of the plant as pure oxygen, (which it actually won't be), the bubble will lose oxygen and gain nitrogen as it rises through the water. In the typical biology lab exercise they set up a large container filled with water that has a lot of sodium bicarbonate as a CO2 source, stuff a bunch of Elodea under an upside down glass funnel, shine a bright light on it, such as a photoflood bulb, and collect the gas that bubbles up the neck of the funnel. What they get probably has a higher percentage of oxygen in it than ordinary air, but it still has a lot of nitrogen._


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## Edward (May 25, 2004)

Squawkbert said:


> We need a way to differentiate high current effects (correlated w/ higher surface agitation) from the effects of lowering O2 conc.
> 
> Any takers?


 Water to air gas equilibrium?


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## defdac (May 10, 2004)

Edward said:


> Pearling? What does pearling indicate in terms of plant health? Nothing.


And what have oxygen bubbles gaining nitrogen from the water to do with plant health? Nothing.

The more light, the more pearling, and more growth.
The more CO2, the more pearling, and more growth.

Rubisco seems fine?


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## Squawkbert (Jan 3, 2007)

Edward said:


> Water to air gas equilibrium?


It has been said that some plants really like some current - my idea was to come up w/ a way to isolate and differentiate any effects that strong current has on plant growth from the effects of various O2 conc.s.


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## Edward (May 25, 2004)

Squawkbert said:


> It has been said that some plants really like some current - my idea was to come up w/ a way to isolate and differentiate any effects that strong current has on plant growth from the effects of various O2 conc.s.


 That must be incredibly difficult to do.


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## Edward (May 25, 2004)

Hi defdac

The post by HeyPK has nothing to do with plant health. I didn't say it does. Still, it is the best explanation about pearling and what pearling is. I think it is worth saving.

Anyway, this thread is also about plants growing in high CO2 not to be able to live in lower CO2 levels. But plants growing in lower CO2 do well in even lower and also high CO2. In simple terms, lower CO2 grows better plants in terms of health and ability to resist algae. High CO2 makes plants vulnerable to algae infestation. This is why we see so many posts about algae in high CO2 aquariums. Makes sense?



Thank you
Edward


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## Salt (Apr 5, 2005)

One problem with running aeration in the tank with lights on is depending on your setup, the bubbles can block light from getting to the plant. I observed quite a dramatic positive response by moving the aeration from _inside_ the tank to an airstone in the HOB filter. (It's an Aquaclear; I used a Dremel tool to create a notch for the airline.)

This also resulted in less CO2 loss. I was able to turn my CO2 injection rate down by nearly 50% and maintain the same levels.


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## Laith (Sep 4, 2004)

Edward said:


> ... High CO2 makes plants vulnerable to algae infestation. This is why we see so many posts about algae in high CO2 aquariums. Makes sense?...


Sorry, but I'm having a very hard time accepting this generalization at face value. Just because people have algae in high CO2 tanks does not mean that the high CO2 makes plants vulnerable to algae infestation.

I have several high CO2 aquariums and as long as I keep up with the plants' higher demand for ferts (due to good light and high CO2), I don't have algae issues.

I'm not implying that you can't have very nice plant growth with lower CO2 levels (I'd recommend staying away from very high light tanks in this scenario); the plants will just use less ferts and grow slower.

I know I've gone a bit off topic re the O2 question but...


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## Edward (May 25, 2004)

Hi Laith
In my experience, plants under very high light, water surface movement and 20 ppm CO2 do not grow slower then plants in 30 ppm CO2 without surface movement. 

Did you read post #1 and the article? It explains why.


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## Laith (Sep 4, 2004)

Sorry, I meant slower growth with lower lighting  .

Yes, I did read the article. Very interesting in that I didn't realize that O2 molecules can block the function of the Rubisco enzyme. You never stop learning in this hobby! 

My point was regarding going from there to here:



> ... High CO2 makes plants vulnerable to algae infestation. This is why we see so many posts about algae in high CO2 aquariums. Makes sense?...


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## Salt (Apr 5, 2005)

I think what Laith is saying is it's not so much "high CO2," but aquariums without aeration.

I've been a big proponent of running aeration in tanks, especially when they're covered, and I've taken a lot of grief for it. ("Bubble walls are like bubbling divers and have no place in a serious tank," "Airstones will cause you to lose all of your CO2," etc.) It's nice to read something that corroborates my personal methods for once.


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## Edward (May 25, 2004)

Salt said:


> I observed quite a dramatic positive response by moving the aeration from _inside_ the tank to an airstone in the HOB filter. This also resulted in less CO2 loss. I was able to turn my CO2 injection rate down by nearly 50% and maintain the same levels.


 I had done the same thing like you and it worked very well. An HOB filter water fall should be sufficient enough for those who dislike air pumps. 

Isn't it beautiful to see perfect plants, happy fish and clean water surface?


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