# newbie question: Doesnt pearling plants counteract co2?



## tradebaron (Aug 20, 2014)

I understand that plants need co2. they use co2 to create oxygen. But doesnt o2 contract co2?
If fish thrive on o2.. i feel bad turning on the co2 as I am taking away their oxygen. But does the co2 I inject fuel the plants to produce more o2?

Sorry I am very new to this hobby..


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## Clownloachlover (Apr 21, 2010)

very good question I await the response as well as I am also new to this whole planted tank situation


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## greenfin (Nov 4, 2013)

Hmm, never thought about it like that. I run CO2, yes the fish wouldn't like it much except it makes my plants pearl and fill my tank with O2. Fish say hooray! So, what's the science (if any) with O2 binding to CO2 and canceling each other out? I just re-read my sentence...no wonder I'm confused! My chemistry is weak but I don't think O2 binds CO2 or anything? Otherwise my fish would be long snuffed. As far as off-gassing CO2, doesn't surface agitation release CO2 out of the tank and allow atmospheric O2 back in? I'm sure that much is true. Et voila le airstone...but only at night.

Some one who knows what they are talking about and can explain it please chime in with a proper answer! 

Sorry clownloachlover and tradebaron. Maybe I would have been better to keep my post un-posted and just wait for the real answer. But I do want to know too!


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## greenfin (Nov 4, 2013)

Okay, found a video by a guy called nickmach007 on you tube that gives a good explanation of the balance between oxygen and carbon dioxide. I believe reckon has put links to his videos in the forum before. Sorr Ion't know how to post a link to a video.


I learned that co2 and oxygen levels do not necessarily relate directly or inversely to each other. I also learned tat increasing oxygen levels can allow your livestock to tolerate higher levels of co2. So you can have surface agitation to increase oxygen in the water and yes you will off gas some co2 but it seems like that's not too high a level of loss. Especially if it's just a rolling ripple from a filter out flow.


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## MDT (Aug 8, 2014)

I do not claim I know everything and I can definitely be wrong, but I believe I can answer this one:

The short answer is no, O2 does not counteract CO2. But before we can answer in greater detail the question of whether O2 emitted by plants counteract CO2 in water, we need to understand how CO2 and O2 behave when dissolved in water.

O2 is a fairly balanced molecule due to it's molecular stability. So even when O2 is dissolved in H2O, it is still retained as a molecule in a dissolved state. Thus, O2 is stable.
CO2 on the other hand is a bit more complicated. For the sake of simplicity, let's just say that when CO2 is dissolved it remains the same and stable, just like O2. (In actuality, it becomes Carbonate, Bicarbonate and Carbon dioxide)

With that understanding, we now know that the molecule, O2, and compound, CO2, do not undergo change when dissolved. Yay!

So then why do we use CO2 in our aquariums? For our plants. CO2 is used for our plants to help convert sunlight and nutrients into sugar for growth, and the byproducts of this chemical reaction, photosynthesis, is O2. O2 is then released into the water and the cycle is complete.

Therefore, O2 is the result of CO2 being added into our water. There is no cancellation, negating or counteracting in place. Without the addition of CO2, you wont have O2 (inside the photosynthesis cycle). This is also true in the reverse. Fish take in O2, emit CO2 and then plants use that CO2 to make O2. Neither CO2 or O2 bind to each other to cancel out there chemical properties. You simply need one to create the other.

It's safe to turn on the CO2 in your aquarium as long as CO2 levels are non-lethal. I believe you might be interpreting the physical effects both CO2 and O2 have on living organisms and associating them as two things that cancel each other out due to the way organisms behave in the presence of each, but as I stated above, it's merely a balance of the two in a cycle.

And onto the question of surface agitation; it does both (release and dissolve) CO2 and O2 into the water. CO2 is way more readily dissoluble in water, but also leaves water pretty fast too.

TL;DR: CO2 and O2 are part of a cycle known as photosynthesis and as long as your CO2 levels are appropriate, it does not hurt your fish. Neither CO2 or O2 counteract each other.


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## tradebaron (Aug 20, 2014)

Wow great answer. Thanks so much for clairfying. Can someopne explain to me how surface agitation helps release and dissolve co2? I heard you didnt want any surface agitation to keep the co2 in.. but I have NO IDEA why. What is the science of it.. and how does co2 dissolve? I just do what I hear but dont understand it completely..


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## greenfin (Nov 4, 2013)

Thank you for your great answer, MDT!

I have no idea how agitation works to oxygenate water but I do know a stagnant pond with no movement has way less oxygen in it than a rushing mountain stream. Having said that, I'm not sure that one or the other has different levels of CO2. They may... Bah! I keep responding to your posts without real answers! From what I gather, moderate surface agitation like one would get from a filter out flow (the standing ripple wave) does off gas some CO2 (ie wasted from our tank/container) but the added oxygen is more beneficial. Running an airstone at night really gets the surface agitated thus releasing built-up CO2 from the day and re-oxygenating the water. Remember, plants use oxygen at night (when not photosynthesizing). If you ran an airstone at high rate during the day, I wonder how much CO2 you would waste and the plants would never get. I bet someone has tested it somewhere.

I have a HOB on some tanks that I run CO2 on and they agitate the surface way more than my tank with a canister filter. However, plants still grow at a good rate in the HOB tanks. I don't pump more CO2 into those because of the filtration difference. So I theorize that moderate surface agitation doesn't off-gas too much CO2.

This is a very interesting thread! You are asking great questions I'd like to know the answers to!


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## MDT (Aug 8, 2014)

tradebaron said:


> Wow great answer. Thanks so much for clairfying. Can someopne explain to me how surface agitation helps release and dissolve co2? I heard you didnt want any surface agitation to keep the co2 in.. but I have NO IDEA why. What is the science of it.. and how does co2 dissolve? I just do what I hear but dont understand it completely..


This is a pretty straightforward one:

Surface agitation releases and dissolves both CO2 and O2.

Yes, it does both, but just at different rates and concentrations. 
Let's only examine CO2 since O2 is another thing to explain and CO2 was your question.



> CO2 on the other hand is a bit more complicated. For the sake of simplicity, let's just say that when CO2 is dissolved it remains the same and stable, just like O2. (In actuality, it becomes Carbonate, Bicarbonate and Carbon dioxide)


The thing to understand about CO2 is that it actually isn't quite that stable. Unlike O2, CO2 is more ready to change it's chemical structure. Let's not get into why because it's complicated, but just know that it isn't as balanced as O2. So because it's so eager to change, it readily dissolves in water AND readily leaves it. It's just constantly looking to change into different forms and states. Note that not every compound of CO2 will change, just that CO2 overall is capable of it rather easily.

So this explains the rate at which CO2 is able to dissolve or leave water. It just readily does it.

What about concentrations? Well the air in Vancouver is composed of approximately 0.03% CO2. You can just google the numbers. That's a really low concentration, so when surface agitation occurs inside a tank with CO2 being injected, more CO2 is ready to leave the water (because there is just more in the water) rather than enter it (because there is less in the air) purely out of concentration. Makes sense?

Thus people will say that you don't want surface agitation if you do not wish to lose your CO2 dissolved in your water. Mind you, if you got a strong supply of CO2 entering your water and being mixed thoroughly, surface agitation shouldn't be a problem and will help your livestock breathe. Remember that it just comes down to balance.

Btw, I would have loved to have bought that tank you were selling ;-;


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## tradebaron (Aug 20, 2014)

Thanks for all your responses.


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