# Some silly questions about CO2 bubbles



## amateurfishkeeper

Hi everyone

I'm new to CO2 and trying to follow the great advice available on this site. Nothing dramatically different has happened since I started using CO2 so I'm experimenting with different variables (lighting, nutrients, flow, CO2 dosing, scheduling etc) to try and find the 'sweet spot'.

But, there are a few things I don't 'get' about CO2. So I use a pressurised system which gets CO2 into the tank and I can see the bubbles circulating around the tank nicely etc. I find some of the information about CO2 I read a bit strange or contradictory. Can anyone help me out with these two questions?

1) If a CO2 bubble rises to the surface of the water and breaks there, does it mean that CO2  bubble added nothing to the tank? The reason I ask this is because I read statements like 'try to keep the bubbles in the water for as long as possible' everywhere. Does this mean we are aiming at keeping bubbles under the surface of the water for as long as possible until they eventually fully diffuse? If, in addition to the bubbles that circulate around my tank I also see a film of bursting bubbles at the water surface as well, is that all wasted CO2?

2) Can a plant only use CO2 if it exists in a fully diffused form? I read statements online like 'aim to have the CO2 bubbles flowing in and around plants. This sounds a bit weird. Are we thinking about bubbles hitting plants? Is this really how plants get access to CO2? Do they need to have bubbles smashing into them or can they only use CO2 when it exists in an invisible form in the water around them?

Sorry if questions are stupid or naive but I find these points hard to understand.


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## tim

Hi amateurfishkeeper, the only silly questions are those not asked 
1 a co2 bubble will dissolve as it rises, so we try and keep them suspended in the water column for as long as possible, once it leaves the surface it adds nothing to the water, any bubbles that exit the tank are wasted co2.

2 plants can absorb co2 that settles on the leaves from what I understand (read may be wrong) this is why people like to use atomisers they create a fine mist which clings to the plants for use.


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## Marcel G

Hi amaterufishkeeper!

Your questions are very good and show that you really think of how it works.
ad 1) CO2 bubbles need time to dissolve in water. The more time you give them, the better. If you are able to keep the bubble in the water for at least 5 seconds, it will dissolve approx. 50% of its volume. As Tim says, the bubbles that get to the surface where they burst are lost (waste) bubbles => this CO2 gets to the air, not to the water.
ad 2) There is a theory that plants may be able to use the CO2 in gas phase (i.e. as bubbles or microbubbles) more effectively that the CO2 in water phase (i.e. fully dissolved). If this theory is true then the CO2 atomizers and diffusers should be better for plants than CO2 reactors. Unfortunately, no one knows ... it's just speculations.


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## Crossocheilus

ardjuna said:


> There is a theory that plants may be able to use the CO2 in gas phase (i.e. as bubbles or microbubbles) more effectively that the CO2 in water phase (i.e. fully dissolved). If this theory is true then the CO2 atomizers and diffusers should be better for plants than CO2 reactors. Unfortunately, no one knows ... it's just speculations.



I have heard this also but being some one who uses an atomizer I would say I see no obvious way this could work, there is no build up of micro bubbles on the underside of leaves for plants to access gaseous CO2. What I do know is that they are easy to use and quick to dissolve CO2, where reactors often need a long time to build up CO2. 

Just my thoughts and experiences on the matter.


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## Jose

http://www.barrreport.com/forum/barr-report/co2-enrichment/1128-co2-issues-read-this

Its not about opinions any more. I urge anyone to try it. Or just look at ADA tanks.


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## Andy D

Jose, an interesting read. 

Have you noticed how Tom advises to position a spray bar - vertically rather than horizontally. Hmmm...


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## Marcel G

Jose said:


> Its not about opinions any more.


Jose, you are a really bad reader!
The post is packed with opinions without showing any "hard data" (experiment results, methodology ...).
Why do you think the CO2 bubbles are better than dissolved CO2? Just because Mr. Barr says it. He did not use any proof, he just said it, and you believe him.
What Mr. Barr says:
"Consistently I _*see*_ better growth ... Why would this mist be better than dissolved CO2? For one thing, it's "pure CO2 gas", which flows much faster than dissolved CO2 liquid ... The flux rate is much faster with pure CO2 gas than CO2 dissolved in water, so the plants get more CO2 and a more concentrated form ... I have been playing around _*trying to figuire out*_ ... The CO2 mist + current _*seems to be*_ the best method ...  I've seen the differences between both the methods (bubbles vs. fully dissolved gas) with the internal CO2 venturis vs the externals. Since the pure gas bubble is under the leaf where most plants have their stomates, the distance is minimized ... The gas can move faster (large factor) ... Many of the plants we keep are amphibous and have _*stomates*_ ... I have a great deal of practial experience and approaches to this, _*not all science*_."

Whatever I do, I see no proofs that CO2 bubbles are better for plant growth than fully diffused CO2 gas. According to Mr. Barr, many aquatic plants have stomates. According to scientists, aquatic plants with submersed leaves have no stomates, so his main argument is wrong in the first place. Also, around the leaves of _*all*_ aquatic plants there is a special boundary layer where all the nutrients (incl. CO2) can move just by diffusion, i.e. very, very, very slowly! So whatever form the CO2 has, it can get through this layer only by slow diffusion. So, whatever Mr. Barr _*says*_, it is no proof! It's just speculation based on his _*observations*_. Maybe one day we will know that for sure, but until someone shows us something more than his speculations, we should call it by proper name. Mr. Barr seems to give more weight to his observations than to proper scientific evidences.


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## ceg4048

ardjuna said:


> According to Mr. Barr, many aquatic plants have stomates. According to scientists, aquatic plants with submersed leaves have no stomates, so his main argument is wrong in the first place.


In the second place, this argument is also somewhat incrorrect. Scientists that MOST aquatic plants with submerged leaves do not have stomates. What Barr stated was that "most of the species that we keep...have them." Scientists have also stated that in some aquatic plants (the ones that do have stomata) the stomata remain permanently open. Some scientists believe (or believed) that stomata found on submerged leaves do not function. Other scientist belive, based on their study that the stomata function properly in some cases, for example in species which incorporate a "gas film" on their leaf surface. Have a look at the results of testing on wetland species and please not the measurement of the presence of stomata on both upper (adaxial) and lower (abaxial) surfaces of these submerged leaves=> http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2007.02318.x/full


Additionally, Barr did not state that the stomata were the only mechanism by which CO2 uptake was facilitated. He specifically quoted a question submitted by a poster and answered directly:

Question asked:
>I can imagine that the bubbles are providing very high CO2 levels at the
>leaf surface where they may touch (do plants have specialized cells on their
>surface that may just suck that CO2 right up? - I don't know...need to look
>it up)....or that there is a very CO2 enriched water region around the
>outside of the bubble that they similarly enjoy. 

Barr's response:
Both

His theory therefore is that even in plants that do not have stomata, microbubbles which make contact and adhere to the leaf surface improve the CO2 concentration level within the boundary layer and reduce the distance the CO2 must travel before being captured by the Rubisco molecule. This reduces the time required for CO2 capture.

We do not know what is is that you do when you state "Whatever I do" and we do not know how that compares to what Barr does, but whatever he does, he definitely sees an improvement when using the mist method. Of course, the specifics of his method may require more clarification, so send him a PM and see if you can compare notes.

Barr is a scientist and he specifically stated in the opening post that his observations were not necessarily proof of concept, but that his results suggest that misting may improve CO2 uptake while at the same time reducing the aqueous CO2 concentration and which therefore would reduce the toxicity to fish, so that's a worthwhile goal.

Cheers,


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## Marcel G

As I said: "We should call it by proper name." That was my point.
Maybe we will find that this theory is correct, but until then it's nothing more than a theory.

As to the article cited, you seem to be as bad reader as Jose. This article deals with growing _*terrestrial*_ plants underwater (i.e. terrestrial plants that were submerged, not amphibious plants that created a true aquatic, submersed leaves). There is a big difference between submerged vs. submersed in this case! So, do you have any proof that most of our aquarium plants with true aquatic (submersed) leaves have stomates? I don't know of any _*aquarium*_ plant with _*submersed *_(= truly aquatic) leaves that has _*stomates*_.

PS: I know that Mr. Barr did studied a biology in university, but this does not assure he is using proper (i.e. scientific) methods. On the contrary, from his posts and speculations he seems to be rather a great pseudoscientists. I asked him many times (publicly as well as by PMs) to show us some results of his experiments, and describe his methodology (how did he came to his "results"), but he never ever did this. Until he will show me his methodology and some serious results of his findings, I will take his words as mere speculations and opinions. That's it.


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## Jose

Ardjuna, its fine if you dont believe nothing that T Barr says thats why you should try it yourself. Hes only done two things for this: change injection method and measured o2. Are your results any more scientific than his? Why? Because you put numbers in a website? No! Sorry.I did it and saw much more pearling and since then Ive only used atomizers. Anyone thats not convinced can just try. Also you normally say that plants can grow with just 10 ppm of co2 and very high light yet I see you are using microbubbles in your experiments. I just say good luck in disproving T Barrs ideas. It turns out he is normally right no matter what theoretic made up explanation you choose to give. Some people here might be convinced by your explanations but I am not. To disprove smthing you should presume that it works first and not the other way around.


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## Jose

T. Barr has explained clearly his methodologies for this experiment which is quite simple. So your general statements about Barr dont apply here.

 T Barr is not giving crappy scientific explanations here  to prove his point. Hes just saying i did this and saw this when measured with an o2 probe. Simple and anyone can do the same. You obviously havent done it.

What about ADA and everyone thinking it was magic?

Why dont you give proof that his theory is wrong Ardjuna. He has shown more proof to prove this than you have shown to disprove it (which is none). To be honest i like it that someone questions everything T Barr says but you are just personally biased by now.


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## Jose

By the way, does anybody know how Tom feels about this nowadays since the link I added was from 2005?


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## Marcel G

Jose, it's fine you believe everything Tom Barr says without questioning it. It's also fine you don't like my arguments. I do not need to convince you. You can believe whatever you want. But everyone has right to express his opinion and put his arguments on the table. That's why I express my opinions. I see no scientific arguments in most of T.Barr's statements, but I see some pseudoscientific baloney in it (for example, T.Barr believes that most aquatic plants have stomates, and bases his pseudoscientific arguments on it to "prove" to us that mist is better than fully dissolved gas). I recommend you to read some plant physiology textbook to understand some concepts better and from scientific perspective (<this one> is very good). Than you will be maybe able to judge whether what T.Barr says is wrong or right, scientific or pseudoscientific. Most aquarists don't like knowledge, and don't like to invest their time and energy into reading. I understand that. It's much faster to read some forum (like barrreport.com) and let someone else to explain it to them. But then don't be surprised that your knowledge may be biased and distorted. It's a religious concept to put experiences over knowledge ... knowledge can be dangerous (it has power to break down everything what you believed so far). I can freely admit my mistake if it shows up that my opinions were wrong. I have no problem with that. If T.Barr shows me some outputs from his experiments (with complete methodology), and the results will be convincing, I'll be the first who will publish it on my website (if he allows). Also, I'm doing a growth experiments right now where I try to find out what concentration of nutrients is truly non-limiting for some aquarium plant species. If I find out that most aquarium plants grow optimally at 30 ppm NO3, then I admit that T.Barr was right. Again, I have no problem with it. Are you able to do the same? And is T.Barr able to admit he was wrong if someone points out his mistakes? And ask yourself few more questions: Are you doing something to find it out? Are you really interested in finding out the truth or is your only goal to advocate T.Barr's claims? I asked T.Barr for publishing his data, but he did not want to. I asked him to explain his methodology, but he did not want to. That's the reason why I decided to do my own experiments to find it out for myself and others (if they are interested). If it shows up that 30 ppm NO3 is non-limiting, hooray! If not, hooray! My primary goal is not to discredit T.Barr, but to find out it for myself ... to verify it. But I admit that I don't like T.Barr's pseudoscientific explanations, and I don't understand why he doesn't want to publish the results of his experiments. That seems strange to me. As if he was hiding something.


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## Marcel G

Jose, do you know how exactly T.Barr arrived to the conclusion that for most aquatic plants 20-30 ppm NO3 and 2-3 ppm PO4 is non-limiting? Can you describe his methodology here? What method he used to find this out? How exactly he proceeded with this experiment? I asked him the same question, but he did not want to explain it in more detail. Also I did not find it explained well elsewhere on the web. Maybe you have access to some other (better) resources. The only thing I was able to find in one of his post was an information that he used LaMotte and Hach test kits for measuring nutrient consumption by aquarium plants in his tanks (this is by far the only information from his "methodology"). What do you think, Jose, is the best method for finding out the real consumption of nutrients in our tanks? Try to be as objective as possible ... don't look at me or T.Barr. If you want to find out how much nutrients your plants need for optimal growth, how would you proceed? For sure, there are several ways to find this out. What method would you chose and why?


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## Jose

Hi Ardjuna, to answer you question: I dont care if 30 ppm is non limiting. Why? Because Ive tried adding more and there is no big difference except maybe if nutrients are precipitating etc. Ive said it many times I dont care about exact values, and yes sure maybe its not 30 but  50 ppm so? No big deal. All I know is I dont get defficiencies in my tank which has unknown ammounts of nutrients but EI was my starting point . Ive never sworn by EI ammounts because I dont dose them, but I do think its good for any beginner to start there.

By the ways thanks a lot for the link.

Now about co2 mist theory. I dont care if he said plants have stomates under water, i care about the difference in plant growth between having mist and not this the biggie and dont get lost in the theoretics. He admits not knowing why/ how this happens. I still think youre looking for any little flaw in Barrs theories to discredit him. Ive tried this theory for myself (with my limitted resources) yet you say  i just choose to believe him. No! I already said before that  youve said you can grow plants in high light with only 10 ppms of co2 and then I saw your tanks and they use co2 bubbles. A bit contradictory right? Since you say this theory doesnt work.


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## Marcel G

Jose said:


> I dont care if 30 ppm is non limiting...there is no big difference except maybe if nutrients are precipitating


If you ever cared, you may find out some interesting things. But since you don't care you are limited just to your/others subjective experiences.
By the way, precipitation is related mainly to iron oxidation in our tanks, not to NO3 concentration.



Jose said:


> I dont care if he (T.Barr) said plants have stomates under water...


Yes, that's obvious. You don't care about what T.Barr says or may prove, but you care a lot of what I say or may prove. What I say is always suspicious, contradictory, or at least "just theoretical". Double standards? Obviously.



Jose said:


> Since you say this theory doesnt work.


No! I don't say this theory doesn't work. I say, that it's just theory. That's difference. If it shows up someday that this theory is right, I'll just accept it. I have no problem with it. I just pointed out that T.Barr's arguments in favor of this theory were wrong and misleading (at least in some aspects). That's all.


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## Manu

Hey guys, if you want to argue, why don't you pm each other and leave this thread in peace? I'm no moderator here but I think this is going a bit too far. I subscribed this thread finding the question very interesting but this argument is not giving anymore answer/help to the OP... Let's keep it peaceful  .
Cheers,
Manu.


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## Chris Jackson

I'd just like to say that when I moved from an UP in line atomiser to a reactor everything in my tank picked up but of course I cannot guarantee that that single change was the cause.

What I can say though is that I hated the look of atomiser mist in my tank and also that I've grown supposedly advanced plants perfectly happily under 150w halides using only co2 bubbled into one of two filters as a reactor.

I want to know what Amano is using in his monster tanks because if they were powered by atomiser mist I'd think they'd look horribly cloudy across over 2m widths?


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## Marcel G

Manu said:


> Leave this thread in peace... this argument is not giving anymore answer/help to the OP...


I think that the original poster got his answer already in the second and third post. Then Jose claimed that the "CO2 mist" theory is not just a theory any more based on T.Barr's pseudoscientific arguments. I think it's perfectly fine to argue these things here. We won't kill each other; we just discuss it. Exchange of views is healthy.

_Colombo: __*Just one more thing.*_
If Jose, T.Barr or anyone else is saying that CO2 mist is better for plant growth, how do you measure it's concentration? How can you be sure that 30 ppm CO2 in fully dissolved form is the same as 30 ppm CO2 in gas form?
If I paraphrase it, you say that if we have two tanks with the same conditions (same volume, same substrate, same plants, same nutrients level ... with only difference being CO2 form), and in the first one we have CO2 mist (in gas form) while in the second one we have fully dissolved CO2 (in aquatic form), then the plants will grow faster/better in the first tank. My question is, how do you measure the _*mist CO2*_ concentration? Do you have any special mist CO2 meter for it? Or how do you know that you have the same concentration of CO2 in both tanks? The only CO2 we are able to measure is the one in fully dissolved (= gas) form. If CO2 is not dissolved yet, we are not able to measure it. Do you get my point? So if it would be true that CO2 mist is better for plants then it would mean that they get _*much more higher*_ CO2 concentration than is the concentration of fully dissolved CO2 in water. And if this is true, then you don't have same conditions in both tanks, so your comparisson is not valid.
Maybe CO2 mist is more effective way of CO2 supply (you supply smaller amount of CO2 gas into your tank to get high CO2 concentration), but if you ensure the same high CO2 concentration in fully dissolved form, the plants may grow just as fast. So again, if you want to compare the plant growth rate using CO2 mist vs. fully dissolved CO2, then you have to ensure the same concentration of both forms in your tank. But there is no way to measure the CO2 mist concentration as all CO2 meters are able to measure just the fully dissolved CO2.


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## Jose

ardjuna said:


> If you ever cared, you may find out some interesting things. But since you don't care you are limited just to your/others subjective experiences.
> By the way, precipitation is related mainly to iron oxidation in our tanks, not to NO3 concentration.


Phosphates as well! which is what I really meant. And I was also reffering to ion exchange although didnt say so.


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## Jose

ardjuna said:


> _Colombo: __*Just one more thing.*_
> If Jose, T.Barr or anyone else is saying that CO2 mist is better for plant growth, how do you measure it's concentration? How can you be sure that 30 ppm CO2 in fully dissolved form is the same as 30 ppm CO2 in gas form?
> If I paraphrase it, you say that if we have two tanks with the same conditions (same volume, same substrate, same plants, same nutrients level ... with only difference being CO2 form), and in the first one we have CO2 mist (in gas form) while in the second one we have fully dissolved CO2 (in aquatic form), then the plants will grow faster/better in the first tank. My question is, how do you measure the _*mist CO2*_ concentration? Do you have any special mist CO2 meter for it? Or how do you know that you have the same concentration of CO2 in both tanks? The only CO2 we are able to measure is the one in fully dissolved (= gas) form. If CO2 is not dissolved yet, we are not able to measure it. Do you get my point? So if it would be true that CO2 mist is better for plants then it would mean that they get _*much more higher*_ CO2 concentration than is the concentration of fully dissolved CO2 in water. And if this is true, then you don't have same conditions in both tanks, so your comparisson is not valid.
> Maybe CO2 mist is more effective way of CO2 supply (you supply smaller amount of CO2 gas into your tank to get high CO2 concentration), but if you ensure the same high CO2 concentration in fully dissolved form, the plants may grow just as fast. So again, if you want to compare the plant growth rate using CO2 mist vs. fully dissolved CO2, then you have to ensure the same concentration of both forms in your tank. But there is no way to measure the CO2 mist concentration as all CO2 meters are able to measure just the fully dissolved CO2.



Lets see Ardjuna, to see the difference between the two forms you only need to inject exactly the same ammount of co2 into the tank. One time dissolve it all and the next time use an atomizer of some sort. The BPS are kept the same so whatever difference you see should be due to the different co2 forms in water because the total co2 injected is the same. So you dont need fancy co2 measuring kits here only a bubble counter. You dont measure the dissolved co2 because as you say this is not measuring the bubbles. This is clearly explained in the link I added.

There are more questions to be answered like:
1) How do plants grow with only co2 bubbles and the least dissolved co2 possible like in ADA tanks?
2) Has the size of the bubbles got any effect?
3) Probably co2 bubbles have less an impact at higher co2 ppm

Toms Barrs experiments show mostly a middle ground where you dissolve quite a lot of co2 but still have micro bubbles.

I like these kinds of conversations even if they look crazy to hobbyists because I think this is where you learn the most.


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## Marcel G

Jose said:


> To see the difference between the two forms you only need to inject exactly the same ammount of co2 into the tank ... whatever difference you see should be due to the different co2 forms in water because the total co2 injected is the same. So you dont need fancy co2 measuring kits.


The problem I see here is that you are comparing the same _*amounts *_of CO2, not the same _*concentrations *_of CO2. I understand what you want to say, and I agree that if you add, for example, 5 grams of CO2 into your tank in the form of bubbles vs. in the form of fully dissolved gas there may be some differences in growth rates. I also agree that we can show the difference (if there is any) by a simple growth experiment with two identical tanks which will differ just by the CO2 form (CO2 mist vs. fully dissolved CO2). This will show us what CO2 form is better for plants.

But as to the concentration of CO2, this experiment won't help. Because if your question was "Do plants grow better under 30 ppm CO2 in the form of bubbles or under 30 ppm CO2 in the fully dissolved form?", then you have no relevant way to measure the concentration of CO2 bubbles. And this was my point. Whenever you measure CO2 concentration in your tank, you measure solely the dissolved CO2. The CO2 in the form of bubbles which are not yet dissolved do not add to this ppm concentration. So if you measure 30 ppm CO2 in your tank where you use a CO2 atomiser (CO2 mist), then this measurement tells you that you have 30 ppm CO2 in dissolved form + unknown amount of CO2 in the "bubble form". And because of this _*unknown variable *_you won't be able to compare it ... in a proper, objective way.

So you say (and maybe you are right, maybe not) that CO2 bubbles pose some advantage over fully dissolved CO2 for plants, but you can hardly compare these two in terms of concentrations. Do you see what I mean?



> There are more questions to be answered like:
> 1) How do plants grow with only co2 bubbles and the least dissolved co2 possible like in ADA tanks?
> 2) Has the size of the bubbles got any effect?
> 3) Probably co2 bubbles have less an impact at higher co2 ppm


ad 1) Whenever there is a CO2 bubble in water, from the very moment it gets out of the diffuser it begins to dissolve in water. So there is nothing like CO2 bubbles without any dissolution. In ADA tanks the dropcheckers are green which means that at least about 30 ppm CO2 dissolved in water. The rest may escape to air, but still 30 ppm CO2 is in the water in the dissolved state.
ad 2) The size of the bubbles has effect on the time the bubble can remain in the water. The bigger the bubble the harder to keep it in the water. Smaller bubbles have more time available to dissolve.
ad 3) This can be as well due to the concentration issue. As the concentration of dissolved CO2 comes close to the concentration of "bubble CO2", the difference is no more as prominent (noticeable). We know that in the bubble the CO2 concentration is ~100% (or a little less due to its impurities). In the water the concentration is much more less. But when the concentration of CO2 in the water reaches the "saturation point" (which may be somewhere around the 40 ppm CO2), the difference plays no role anymore.


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## Jose

ardjuna said:


> So you say (and maybe you are right, maybe not) that CO2 bubbles pose some advantage over fully dissolved CO2 for plants, but you can hardly compare these two in terms of concentrations. Do you see what I mean?



I see what you mean but it doesnt make sense to me. How can you measure efficiency of two ways of co2 diffusion if total co2 going in is different because you need to get the same dissolved ppm? I think maybe what you want to know is what works better, if 30 ppm (dissolved) with mist or 30 ppm (dissolved) w/o mist am I right? Well if the theory discussed is right then 30 ppm (dissolved) with mist will work better (Think about it). Why? Because if with same co2 ammount injected mist works better then for the mist method we will need more co2 to get the same ppm (dissolved) yet the effect will still be better. You would be adding more co2 with the mist method as to get more dissolved co2.

Basically you cannot measure concentration because this depends on the diffusion method and you actually want to know which method is best in growing plants. Concentration is not independent here, total co2 used is. You have to choose a variable that stays constant for both methods.



ardjuna said:


> ad 1) Whenever there is a CO2 bubble in water, from the very moment it gets out of the diffuser it begin to dissolve in water. So there is nothing like CO2 bubbles without any dissolution. In ADA tanks the dropcheckers are green which means that at least about 30 ppm CO2 dissolved in water. The rest may escape to air, but still 30 ppm CO2 is in the water in the dissolved state.



Yes, this is why I said minimum dissolved co2, because there is always going to be some dissolved. I think ADA is the least efficient mist method in dissolving co2. ADA levels are not high at all and I bet they keep climbing through the day (look at surface movement). so they might be 30 ppm (dissolved) at the end of photoperiod and maybe 5 at the start. ADA in Japan never uses a dropchecker, but ADA in Poland etc do. Dropcheckers here dont say nothing because they will measure all co2 in the water weather dissolved or in bubbles.



ardjuna said:


> ad 2) The size of the bubbles has effect on the time the bubble can remain in the water. The bigger the bubble the harder to keep it in the water. Smaller bubbles have more time available to dissolve.


Yes, but I mean subtle changes in the size of the bubbles whilst keeping them small enough to travel around the tank. Subtle changes in size might have an impact and there might be an "ideal size". There is no proof for this and its just a question I ask myself.



ardjuna said:


> ad 3) This can be as well due to the concentration issue. As the concentration of dissolved CO2 comes close to the concentration of "bubble CO2", the difference is no more as prominent (noticeable). We know that in the bubble the CO2 concentration is ~100% (or a little less due to its impurities). In the water the concentration is much more less. But when the concentration of CO2 in the water reaches the "saturation point" (which may be somewhere around the 40 ppm CO2), the difference plays no role anymore.


You dont know this. Concentration in a CO2 bubble is approx 1964ppm. You cant reach this conc in water so you cant know the effect of bubbles at different co2 ppms (dissolved) if you dont do the experiments. The role the bubbles play might be less each time as conc goes up but you cannot say they wont play a role. Even if the role is not important it doesnt matter because we are more interested in the role it plays from 0 to 30 ppms (dissolved) because the idea is to have less dissolved co2 in our tanks as to make it safer for fish etc.
It looks like if anything is non limitting it might be the conc in a co2 bubble. Maybe Im wrong and it turns out 80 ppm of co2 is the same as the mist method. But the mist method would still be safer and simpler.


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## Jose

ardjuna said:


> "Do plants grow better under 30 ppm CO2 in the form of bubbles or under 30 ppm CO2 in the fully dissolved form?"


If you are comparing ppm then they have to be mg of co2/1 Kg of water. This is not the case of a bubble so what you want to compare is not comparable. Totally different things.

ppm of the water=mg of co2/1 Litre of water
ppm for a bubbles= mg of CO2/1 Litre of CO2

There is no such thing as 30 ppm of co2 in the form of bubbles.


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## John S

Andy D said:


> Have you noticed how Tom advises to position a spray bar - vertically rather than horizontally. Hmmm...



I noticed that too Andy. I've not seen any tanks on here with that configuration but as this was 10 years ago, maybe horizontal has been proved to be better?

Hope Jose and Ardjuna don't mind me interrupting.


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## Jose

John S said:


> Hope Jose and Ardjuna don't mind me interrupting.


, I hope more people interrupted even.


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## Andy D

John S said:


> I noticed that too Andy. I've not seen any tanks on here with that configuration but as this was 10 years ago, maybe horizontal has been proved to be better?



One day when I start using externals I'll give it a go. 

My internals don't allow me to try it.


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## xim

John S said:


> I noticed that too Andy. I've not seen any tanks on here with that configuration but as this was 10 years ago, maybe horizontal has been proved to be better?
> 
> Hope Jose and Ardjuna don't mind me interrupting.



Has anyone seen Tom Barr use a spray bar in any of his tanks? Really, spray bar vs nozzle, which one is better is just a preference, not a fact.


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## John S

xim said:


> Has anyone seen Tom Barr use a spray bar in any of his tanks? Really, spray bar vs nozzle, which one is better is just a preference, not a fact.



Nobody was talking about nozzle v spray bar. It was the orientation of the spray bar that was mentioned by Tom.


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## Wizard

Mine is vertical , 
the spray bar is in the top right corner vertically, with the flow pointing towards the middle of the tank , the filter part of the pump has a plastic shroud which I have drilled a hole to insert my co2 pipe , i m running a diy kit using yeast, and the bubbles being produced are tiny, the pump is horizontal in the tank so the co2 entering it sits with the water flowing through it before it builds up enough to be sucked through and blown out the spray bar 

Im quite surprised how fast the plants are growing , every day I can seethe amount of growth


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## Wizard

Like this


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