# Equlibrium Co2 and air injection



## f1ea (Jul 7, 2009)

Hi all,

I have a couple of questions about Co2 loss in a low tech planted tank and i hope you guys can help me out.

Just bought an additional powerhead (400 GPH) with the quick filter to improve tank conditions and battle BGA. For this reason I want to increasing oxygen levels with the optional airline tubing, as it draws a considerable ammount of air. However i am not entirely convinced on whether to use the airline or not.

- In a non-Co2 injected tank (Excel only), is the ammount of Co2 lost to air bubbles relevant or is equilibrium Co2 more important, and will occur pretty much regardless of surface agitation (provided it is not excessive)?
- Is it more beneficial to have the extra O2 and gas exchange than whatever Co2 is lost?
- There's more Co2 in air than water, by injecting air am i not also introducing Co2?

My water is GH 13, KH 7, pH 8, temp 82 F. Tank is 200 Gal, and i use the following filtration equipment:
1) 400 GPH canister filter
2) 200 GPH powerhead (no filter, no air intake)
3) 400 GPH powerhead (filter + air intake)

Thanks in advance!


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## bradac56 (May 9, 2007)

C02 loss is nearly irrelevant since your plants are taking in less C02/02 and nutrients do to less light levels - less demand equals less worry.

I run sponge filters or hamburger filters on all of my low-light tanks so the 02 levels are fine but more 02 can't hurt anything.

- Brad


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## ianryeng (Dec 22, 2008)

The short answer, Excel is not co2. It provides a soluble source of carbon for the plants. Air injection should not overly affect this but it will reduce what free co2 there is that occurs naturally in your water...

I believe that air is more easily soluble in water than co2, the ratio of off gas when you inject air into the water leaves more o2 than co2 (which makes sense as co2 is a more complex hydrocarbon).

What I am not sure of is what the reason you want to inject air into your tank...?


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## Zapins (Jul 28, 2004)

CO2 is far more soluble then air in water because it reacts with water unlike air. It is hundreds of times more soluble actually, this reaction is what causes the pH to drop. CO2 reacts with water to make carbonic acid. Unfortunately, CO2 gas itself is easily dislodged from the water column with any kind of agitation, once there is no CO2 gas in the water, the carbonic acid un-reacts with water and changes back to CO2, which is kicked out the water causing more carbonic acid to convert to CO2. Ultimately you remove nearly all CO2 from your tank in all its forms, which isn't so good for plants.

In a low tech tank, with reduced growth rates, you probably won't see that much of a difference for a short term duration, but if you ran the bubbler for a long time then you might start to see a virtual halt on plant growth.

I agree with ianryeng - why do you want to add a bubbler? BGA is a nitrogen fixing bacteria and thus it does well when nitrates are in very low amounts. If you add more nitrates to the tank it will allow the plants a chance at growth. Also, nitrogen's presence in the water causes BGA to go dormant again. Increasing the current in your tank might be a good idea though since it will dislodge the BGA from any surface it tries to grow on.


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## f1ea (Jul 7, 2009)

Thanks for the responses.

A little clear up: i do not want to inject AIR into my tank; i want to increase oxygen levels because BGA likes low oxygen areas. Since my tank is fairly deep (24"), maybe the bottom is not well oxygenated because most of my BGA accumulates on the substrate, so it is possible. So far, i've never seen a single fish gasping at the surface; but they rarely swim at the bottom either so i guess i can't really tell... 

Also, i am NOT using a bubbler (airstone), i am using an airline feed to the powerhead discharge. It vacums some air from outside and mixes it with the flow discharge. The result is not really a bunch of bubbles reaching to the surface and creating splash, but rather a large ammount of tiny bubbles that pretty much disolve (?) in the water before they hit the surface. The main component is not the air bubles, but rather the 400 GPH of circulation... with some extra fresh air (O2, and maybe some Co2 as well??), because more oxygen is rarely bad.

So in general, i am trying to increase circulation (and while at it, oxygen levels) to be able to fight off BGA (as well as increasing my KNO3 dosage) and improve tank conditions as a whole. 

Because I am not using pressurized Co2, but rather excel, i'm trying to figure out if whatever Co2 is lost due to agitation is ignorable, thus making the oxygen injection feasible; or if some Co2 and/or o2 from the external air might be able to dissolve in the water column.

I understand this is probably still a debatable subject.... and this is why the forum is great! but i hope i explained my intentions clearly 

Thanks again!


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## Zapins (Jul 28, 2004)

With your method, perhaps you won't lose as much CO2 from the water as you would with a conventional bubbler. So it is feasible the way you describe it.

While its true that more O2 is rarely harmful to fish tanks, why would you want to increase the O2 level? The fish's choice of swimming depth is probably a bad indicator of O2 levels since most fish have a built in preference for where they will swim in the water column. Cichlids tend to prefer the lower regions, live bearers and tetras tend to swim in the mid and upper regions and rarely visit the bottom.

Where did you get the information on BGA growing in low oxygen environments (just curious)? From what I know, BGA is an aerobic photosynthetic bacteria (it needs O2 to live), so it makes sense that it shouldn't do well in low air environments. Since it also nitrogen fixes, and nitrogen fixation requires anaerobic conditions they solve this problem by having specialized cells called heterocysts which have thick walls impermeable to oxygen, in which nitrogen fixation can occur.


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## f1ea (Jul 7, 2009)

Zapins said:


> With your method, perhaps you won't lose as much CO2 from the water as you would with a conventional bubbler. So it is feasible the way you describe it.


Yeah, it does seems like the air bubbles are getting dissolved before and within the water column. The air enters at the powerhead output, but i made sort of a spray bar where the air mixes with the water output before it exits; so far it seems efficient, except maybe a little bit less total flow.....



> The fish's choice of swimming depth is probably a bad indicator of O2 levels since most fish have a built in preference for where they will swim in the water column. Cichlids tend to prefer the lower regions, live bearers and tetras tend to swim in the mid and upper regions and rarely visit the bottom.


Exactly, they dont really spend much time on the bottom, so i wouldn't know. The only mid/bottom fish i have are Serpae tetras and a Red tail shark. And they seem ok.



> Where did you get the information on BGA growing in low oxygen environments (just curious)? From what I know, BGA is an aerobic photosynthetic bacteria (it needs O2 to live), so it makes sense that it shouldn't do well in low air environments. Since it also nitrogen fixes, and nitrogen fixation requires anaerobic conditions they solve this problem by having specialized cells called heterocysts which have thick walls impermeable to oxygen, in which nitrogen fixation can occur.


I read it here:
http://www.aquariumslife.com/headline/blue-green-algae/

Here's the oxygen bit (taken from the page above):

_"...In most cases, the ideal location is a dead spot with low oxygen, low water movement and lots of organic waste.

Prevention
Dose nitrates (NO3), add powerheads to aid circulation, frequent partial water changes, do not over-feed and make sure your substrate (if any) is well oxygenated.

Treatment
Oxygen: As a result of the complex chemical process that allows it to fix its own nitrogen, oxygen is toxic to the Blue Green Algae (this is actually why it likes death spot and low oxygen). Increasing oxygen level in the tank will help a lot."_

Thanks again!


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## El Exorcisto (Aug 10, 2006)

In a non-injected tank you run no risk of blowing off CO2. As to oxygenating the lower regions of your tank, I can't think of a better way than putting a powerhead with the venturi hooked up, blowing around the bottom of your tank.


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## Zapins (Jul 28, 2004)

That page seems to sum up BGA quite well. However, the writer doesn't directly suggest adding bubblers to increase O2 concentration in the water. I don't think you can significantly increase O2 concentration in the water using a bubbler since O2 doesn't dissolve into our tank water at more then about 8 ppm O2 at normal 78F temperatures. CO2 enters the water with a CO2 tank because it forms carbonic acid which is very soluble in water, the bulk of the CO2 in the water is in acid form. O2 doesn't react with water so it can only dissolve into the water as a gas which isn't very soluble in water.

H2O2 kills it for sure, but not because it makes regular O2. Perhaps that is what the writer meant by oxygen being useful in killing it. H2O2 breaks apart into a free radical oxygen which is very destructive to cells. The oxygen radical essentially bonds with anything near it tearing whatever it bonds with apart. Normal O2 we breath doesn't do this. The interesting part about dosing hydrogen peroxide is you usually see a steady stream of bubbles rising from the dosed spot. These bubbles are a result of the cell's defense mechanisms. All aerobic cells make H2O2 naturally in small amounts and so they had to develop a way to neutralize the H2O2 before it split apart and formed destructive radicals. The result is an enzyme called catalase whose purpose is to neutralize H2O2 before it forms radicals. When we spot dose H2O2 we essentially overwhelm catalase's ability to remove H2O2 and the extra H2O2 damages the cell and kills it.

Also, as for the CO2 degassing problem. If you don't add CO2 to the water via CO2 tank there is still a small level of it in the water, if I remember correctly its around 3 ppm CO2. If you frisk the water too much the 3 ppm will be jostled out of the water faster then CO2 enters. You will drive down the CO2 level close to 0 ppm which will slow the growth down to a virtual hault. Bubblers won't affect excel, but then again not all plants use excel as efficiently. Some can't use it at all, and others love the stuff (like HC).

Anyways, just some thoughts.


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## GmoAndres (Oct 18, 2004)

Hi!
look this link:

http://www.aquaticplantcentral.com/...-discussions/66594-raising-oxygen-levels.html

Greetings!


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## f1ea (Jul 7, 2009)

El Exorcisto said:


> In a non-injected tank you run no risk of blowing off CO2. As to oxygenating the lower regions of your tank, I can't think of a better way than putting a powerhead with the venturi hooked up, blowing around the bottom of your tank.


That's what i'm doing. Not a bubbler/airstone. I just want to make sure it works and oxygenates the water without driving ALL Co2 out. Basically, the intention is to keep 'equilibrium' Co2 (which is pretty low anyway) and have the extra Carbon provided by Excel, which does not gas out.



zapins said:


> Also, as for the CO2 degassing problem. If you don't add CO2 to the water via CO2 tank there is still a small level of it in the water, if I remember correctly its around 3 ppm CO2. If you frisk the water too much the 3 ppm will be jostled out of the water faster then CO2 enters. You will drive down the CO2 level close to 0 ppm which will slow the growth down to a virtual hault. Bubblers won't affect excel, but then again not all plants use excel as efficiently. Some can't use it at all, and others love the stuff (like HC).


That's the interesting part: would one be able to gas out ALL Co2 (for example with a bubbler) or will the 2-3 ppm of equilibirum Co2 be maintained (in the form of carbonic acid), even with the surface agitation?


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## Zapins (Jul 28, 2004)

You will degas nearly all of it since carbonic acid takes time to form and it is the equilibrium of reacting to form carbonic acid and unreacting to form CO2 that allows CO2 to be maintained in the water at 3 ppm. If you remove all the CO2 gas by shaking the water then there is no time for the reaction to carbonic acid to occur and equilibrium shifts towards CO2 being formed (which is jostled out of the water).

Sorry if I'm not being clear, I haven't slept more then 4 hours in the last few days so I'm a bit out of it. I can draw a diagram later on if anyone wants to see.


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## Diana K (Dec 20, 2007)

I remember seeing a chart of the gph from a power head with and without the venturi. The venturi connection reduces the gph, so check all the specs you can find for the brand of PH you are using to see if there is less water movement in the tank from that particular power head when you are connecting the air tubing to the venturi port. The question might be: is it better to get more gph of water movement or better to add bubbles via the venturi? Is it better to keep the PH aimed down to increase water movement in the lower areas? Is more surface agitation what you need? 
Probably the only way you are going to get these answers is a direct test for dissolved oxygen levels. 
Set up the equipment, run it long enough to have an effect and test AM and PM to see what those levels might be, and if the plants' diurnal cycle affects it. 

If you are seeing very fine bubbles from the powerhead, and not much more than gentle ripples at the surface then you are probably getting maximum air (all its components) dissolved in the tank water, and the least amount of loss to the air above the tank. 

How the individual water/air chemistry happens is probably a good area for more research. Good question:
Does adding very fine bubbles of AIR increase the CO2 in the water? Does it increase the O2 in the water? 
Good point that Zapins is making that each component of the air also undergoes some chemical changes with the water so that each item will be found at a different concentration depending on the surface agitation and other things.


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## f1ea (Jul 7, 2009)

Diana K said:


> I remember seeing a chart of the gph from a power head with and without the venturi. The venturi connection reduces the gph, so check all the specs you can find for the brand of PH you are using to see if there is less water movement in the tank from that particular power head when you are connecting the air tubing to the venturi port.


Yes you are right. There definitely is less flow with the venturi. There is also a bit of flow reduction from using the spray bar and the pre-filter, it has to do with energy loss. Kind of a compromise.



> The question might be: is it better to get more gph of water movement or better to add bubbles via the venturi? Is it better to keep the PH aimed down to increase water movement in the lower areas? Is more surface agitation what you need?
> Probably the only way you are going to get these answers is a direct test for dissolved oxygen levels.
> Set up the equipment, run it long enough to have an effect and test AM and PM to see what those levels might be, and if the plants' diurnal cycle affects it.


I dont have a way of measuring dissolved O2. But for sure, the substrate does better with some extra oxygen... the way i have it set up, is the spray bar is aimed to the surface, but at the end of the bar i have an elbow aimed to the substrate. The flow coming from the spray bar is less than what's exiting the elbow, so it doesnt create much turbulence on the surface.



> If you are seeing very fine bubbles from the powerhead, and not much more than gentle ripples at the surface then you are probably getting maximum air (all its components) dissolved in the tank water, and the least amount of loss to the air above the tank.


Yup, that's what is happening. The fine bubbles do reach the surface, but they are very small and thus float slower than larger bubbles, so there is very litle disturbance.



> How the individual water/air chemistry happens is probably a good area for more research. Good question: Does adding very fine bubbles of AIR increase the CO2 in the water? Does it increase the O2 in the water?
> Good point that Zapins is making that each component of the air also undergoes some chemical changes with the water so that each item will be found at a different concentration depending on the surface agitation and other things.


Yes, i think this is the key. So far i have found mixed opinions... but nothing really definitive. Except that the less surface disturbance the more co2 you will keep. So whatever we do, if we want to keep some Co2 is best to avoid excessive disturbance.

Perhaps by checking pH/kH with the powerhead + venturi operating, and at the same time but different day, without the venturi. It might give some idea of Co2 concentration......

But the ultimate test will be to see plant progress/growth. Because plants could just steal the co2 from the flowing air bubbles without it having to dissolve in the water (this Co2 would not be picked up by testing the water). I think i will be able to tell some difference within a week or so.

Thanks for the comments


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## Zapins (Jul 28, 2004)

Diana K said:


> How the individual water/air chemistry happens is probably a good area for more research. Good question:
> 
> Does adding very fine bubbles of AIR increase the CO2 in the water? Does it increase the O2 in the water?


I believe very fine bubbles of air will increase CO2 levels in water since more air is coming into contact with the water. The tiny bubbles have a lot of surface area, so any CO2 gas inside the mini bubbles will have more area to react with the water. Also, the tiny bubbles remain in the water longer then huge bubbles and so this allows more time to form carbonic acid. The key here is that the bubbles are so tiny that they don't disturb the surface water. Degassing doesn't happen due to turbulence. As for how much of an increase? I don't know, but I don't think you'll get a huge difference. Possibly from the normal ambient 3 ppm to perhaps 5-7 ppm, though someone would really need to test this.

Oxygen levels will increase slightly as well since the small bubbles actually take up room in the water there will be more O2 in the water too. But temperature is really the determining factor in the amount of O2 in the water. What adding air to the tank will do is replenish the O2 used by plants and fish quickly so you will have O2 levels constantly at the saturation point (determined by the temperature) versus having O2 levels fluctuate throughout the day and night as fish respiration and plant respiration changes.



> Perhaps by checking pH/kH with the powerhead + venturi operating, and at the same time but different day, without the venturi. It might give some idea of Co2 concentration......
> 
> But the ultimate test will be to see plant progress/growth. Because plants could just steal the co2 from the flowing air bubbles without it having to dissolve in the water (this Co2 would not be picked up by testing the water). I think i will be able to tell some difference within a week or so.


You probably won't be able to use the pH/KH relationship to determine the changes in CO2 levels in the tank. The difference of a few ppm CO2 won't really affect the pH or KH that much, certainly our test kits aren't accurate enough to detect such a small change.

As for the plant growth, you might see a small difference. Plants aren't likely to take CO2 from passing bubbles though since there exists a barrier of water around every surface in the tank that remains virtually still. A bubble wouldn't get close enough the a leaf or plant to actually touch it and give CO2 to the plant. For CO2 to reach plant tissue it needs to be dissolved. In this form it will diffuse across the dead zone (since the water around plants is more CO2 deficient then water column water as the plants are using the CO2 around them) and be absorbed by the plant.


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## f1ea (Jul 7, 2009)

Zapins said:


> I believe very fine bubbles of air will increase CO2 levels in water since more air is coming into contact with the water. The tiny bubbles have a lot of surface area, so any CO2 gas inside the mini bubbles will have more area to react with the water. Also, the tiny bubbles remain in the water longer then huge bubbles and so this allows more time to form carbonic acid. The key here is that the bubbles are so tiny that they don't disturb the surface water.


This is good. That's what i have been trying to achieve (as a side benefit); the main purpose is to improve water flow/circulation, but if i get some Co2 in the process then all the better!

But i tell you, the bubbles i'm getting are VERY small. Some disolve on their way to the surface, others reach the surface, but they are so small it doesnt create much turbulence. The surface does look like its circulating (i can tell by watching debris) and there are some small ripples (created by the flow of water, not the bubbles).

For the moment, i'm not going to able to tell how much oxygen is being introduced. But at least some will... my fish never gasp at the surface and BGA should not be 'killed' by oxygen (as you mentioned above, there has to be some confusion with Hydrogen Peroxyde)... for BGA i'm increasing KNO3.



> You probably won't be able to use the pH/KH relationship to determine the changes in CO2 levels in the tank. The difference of a few ppm CO2 won't really affect the pH or KH that much, certainly our test kits aren't accurate enough to detect such a small change.


Yes... i have a hobby-grade Tetra Laborett kit, so i dont think there will be much to notice from readings... I could MAYBE pick up some small pH change to give me a general idea. Anyways, i'm not aiming for 15ppm here, my main C comes from Excel.



> As for the plant growth, you might see a small difference. Plants aren't likely to take CO2 from passing bubbles though since there exists a barrier of water around every surface in the tank that remains virtually still. A bubble wouldn't get close enough the a leaf or plant to actually touch it and give CO2 to the plant. For CO2 to reach plant tissue it needs to be dissolved. In this form it will diffuse across the dead zone (since the water around plants is more CO2 deficient then water column water as the plants are using the CO2 around them) and be absorbed by the plant.


Good. Then every usable Co2 should get dissolved (and therefore readable from the water column). Many bubbles do stick to the plant leaves, so it gives more time to dissolve any available Co2...

:thumbsup:


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