# CO2 Questions - Trying to wrap my mind around it



## rpadgett37 (Jan 1, 2014)

I've read a bit on the CO2 topic here and elsewhere and have just a few questions for clarification. This area seems like a very tricky balancing act and as this is my first time using a CO2 diffuser in a tank, I need to get this straight.

My set up:

6.6 gallons
Up-Aqua CO2 system
Baseline Ph: 7.6
Baseline kh: 30 ppm

1. The dumbest question first. ppm is independent of the amount of water, correct? 15ppm of CO2 in 75 gallon is the same as 15ppm of CO2 in my tank. The only differing bit is the amount of CO2 needed to achieve the desired CO2 amount.

3. I just set up the CO2 unit in my tank. I plan to run it for 24 hours before checking CO2 levels. I am running roughly 1 bps and the CO2 is entering the tank at a small trickle.

Tested the water this morning after 24 hours and right out of the tank. I was surprised to see that the bottom fell out from under both the PH (dropped from 7.6 to 5.9) and KH (Nutrafins kit doesn't give a specific number, so it dropped from 30 ppm to between 0-20 ppm, likely below 10).

Given these parameters for the calculation at a given temp of 78 degrees, the CO2 ppm came in at an average of 18 ppm.

I want the ph at around 6.8 - 7 min and max with a kh of 50-60. These values will set the CO2 levels in my tank at around 14ppm given a flow of 1bps. I use an acid and alkaline buffers when needed made by Seachem and know how much of each to use to achieve the desired ph. Kh, however, if it is possible to raise it independent of Ph, I have not a clue what to do.

Could use some help here. As for the rest, does what I am planning here sound right? Suggestions please.

I am only doing water chemistry here. I am setting it up before I add anything but driftwood to the tank. Once water parameters are set and stable, I will then add plants and watch the chemistry, then silent cycle the tank again watching the chemistry, and once reasonably perfect, then and only then the fish.

Thanks in advance. I know there's alot here, but I have much to learn.


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## lilnaugrim (Mar 27, 2013)

1. Yes, you are correct.
2. where's the question? lol np
3. Sorry, can't answer much else here.

So, let me get this straight, you're running purely a tank with no decor, plants, gravel or nothing with CO2 injection? While you'll know how much co2 you're putting out, that's going to change when you get plants in there, as they eat it up, some will take more than other's which will change your count. Might not change your BPS but it will still regardlessly change.

Everything looks alright and like you're on the right track but I would get plants in there as soon as possible, let the tank stabilize before putting fish in. Not so much to stabilize for the Nitrogen Cycle or anything, but to get a feel on your new co2 and the difference it will make with the plants in the tank. Once you have the feel for it and your plants are doing great, I would then add in fish.

Let me know if I completely disregarded one of your questions or something I said sounded not right lol I apologize, I'm a little scatterbrained at the moment.


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## rickey (Jul 7, 2013)

2) I'm just guessing here, NO
3)A kH of 30 ppm (Part Per Million) is way to low to inject CO2. Never be able to hold any kind of stable numbers at those levels.

R


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## peachii (Jan 6, 2013)

http://www.saltyshrimp.de/english/

You can use the salty shrimp products to stabilize your PH and KH to what it needs to be for your fish. A lot of fish keepers who use RO water use this to make the water perfect for certain types of shrimp.


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## rpadgett37 (Jan 1, 2014)

Never could count 

I will do as you suggest with the plants. When I think about it, that makes alot more sense. 

A question about that. As CO2 drops to 0 from the plants eating it, do I then raise the bps to a ppm above the 0 just to ensure there is adequate CO2 in the water?

Thanks very much. You've covered it for me nicely. I now understand that trying to get everything exactly precise and perfectly balanced will be an exercise in futility. That's especially bad for me as I have no hair to pull out 

I'll post an update or additional questions here. Thanks again


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## rpadgett37 (Jan 1, 2014)

rickey said:


> 3)A kH of 30 ppm (Part Per Million) is way to low to inject CO2. Never be able to hold any kind of stable numbers at those levels. R


Good to know!!! That seems kind of important


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## lilnaugrim (Mar 27, 2013)

rpadgett37 said:


> Never could count
> 
> I will do as you suggest with the plants. When I think about it, that makes alot more sense.
> 
> ...


Oh lol, no worries, I'm an artist not a mathematician either.

As for the plants and your bps, it depends. If your plants are doing well with what you've got it at and you aren't seeing any other negative effects, keep it there. If you see they aren't growing as fast as they should be or not as well, bump it up a little. Its kind of like balancing on a seesaw, just watch your plants and how they react and that will tell you to balance one way or another.

I haven't delved into the specific numbers or anything, Rickey would be able to tell you more about the specifics. I'm only scratching the surface here I know.


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## rpadgett37 (Jan 1, 2014)

lilnaugrim said:


> Oh lol, no worries, I'm an artist not a mathematician either.
> 
> As for the plants and your bps, it depends. If your plants are doing well with what you've got it at and you aren't seeing any other negative effects, keep it there. If you see they aren't growing as fast as they should be or not as well, bump it up a little. Its kind of like balancing on a seesaw, just watch your plants and how they react and that will tell you to balance one way or another.
> 
> I haven't delved into the specific numbers or anything, Rickey would be able to tell you more about the specifics. I'm only scratching the surface here I know.


I don't really think I need to be a complete expert here. Just get it in the ball park which with what I've read, what you guys have said (girls too if I missed anybody), and what I am doing (experimenting with really...trial and error to be sure) and I think I'll be fine. Given the not terribly precise nature of the tests I am using, I think the only way I can get any more precise once I am really close is to swish the buffers around in my mouth, then blow across the surface of the water.

I did end up starting over as I read the CO2 kit instructions (leave it to a man to become an expert before reading any instructions). It says 1 bubble every 3 seconds, not 1 bps. Needless to say, my water was so saturated with CO2 I was gasping for air by just looking at the aquarium. So, back to the baseline and give it another, more informed, go.

I'll return to this once I have a bit more to go on. I truly want a happy tank for my Betta I plan to get. If there is such a thing as a Green Dragon, that's what I will search for. If not, well...there are certainly lots of options for my soon to be friend HMPK.

Blessings.


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## amphirion (Jan 15, 2014)

With ppm (parts per million), it is a measurement of concentration. 15 ppm of CO2 in a 10 gallon tank is the same concentration as 15 ppm in a 75 gallon tank. However, the actual number of CO2 molecules found in the 75 gallon will be a couple of magnitudes higher than a 10 gallon. Using the C1V1=C2V2 formula where C= concentration, and V= liters, you will realize that a larger volume of CO2 must be injected into the 75 gallon tank to reach the same concentration found in the 10 gallon.


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## lilnaugrim (Mar 27, 2013)

+1 to amphirion!

And yes there is such things as green dragons technically. Green is a weird color where under lights, your fish is going to look blue but without them they will be green. There is also turquoise, I have a PK who is turquoise and he's got quite a bit of green on him. His picture is in my album under my profile page if you wish to see him.


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## rpadgett37 (Jan 1, 2014)

lilnaugrim said:


> +1 to amphirion!
> 
> And yes there is such things as green dragons technically. Green is a weird color where under lights, your fish is going to look blue but without them they will be green. There is also turquoise, I have a PK who is turquoise and he's got quite a bit of green on him. His picture is in my album under my profile page if you wish to see him.


Gorgeous. Lovin it.

Good news on my chemistry. Reduction of CO2 flow to 1 bubble every 6-7 seconds and buffering with 1 to 2 ratio of Acid to Alkaline buffers has stabilized (more or less) my numbers at PH 7, KH 40ppm, and CO2 concentration 6 ppm.

The unfortunate part in this story is I have to constantly monitor my CO2 flow. Being such a small system, the flow rate varies with external temp changes. I need to find some kind of insulator for the tiny tank of CO2 to the keep the temp more stable.

Any ideas?


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## amphirion (Jan 15, 2014)

2 possible choices: 1) get a stronger heater or 2) move the tank to a better insulated room not subject to a large change in temp shifts.

Furthermore, planted tanks should always be around the acidic side. Natural water is not 7 but more actually 6.5-6.8, due to dissociation of H2O to make H+ and OH-. Adding CO2 will just increase the acidity of the system of carbonates and bicarbonates. However the water chemistry will normalize back to the original perimeters once the gassing is turned off. Therefore it is important not to try to adjust the water chemistry back to 7 (again, not ideal for most planted tank settings) during injection because this will prevent the CO2 from being accessible to the plants because it would rather bind to H+ instead provided by the buffers. This also causes problems when the CO2 is turned off at night and there is no more CO2 for the buffers to act upon which can potentially swing your pH to undesirable levels.


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## rpadgett37 (Jan 1, 2014)

amphirion said:


> 2 possible choices: 1) get a stronger heater or 2) move the tank to a better insulated room not subject to a large change in temp shifts.
> 
> Furthermore, planted tanks should always be around the acidic side. Natural water is not 7 but more actually 6.5-6.8, due to dissociation of H2O to make H+ and OH-. Adding CO2 will just increase the acidity of the system of carbonates and bicarbonates. However the water chemistry will normalize back to the original perimeters once the gassing is turned off. Therefore it is important not to try to adjust the water chemistry back to 7 (again, not ideal for most planted tank settings) during injection because this will prevent the CO2 from being accessible to the plants because it would rather bind to H+ instead provided by the buffers. This also causes problems when the CO2 is turned off at night and there is no more CO2 for the buffers to act upon which can potentially swing your pH to undesirable levels.


Item 1: Had a brain fart earlier this morning. Temp is stable. I am betting it is a little bounce back on the release valve. As I said, a tiny not-so-precise CO2 system. relatively easily remedies with a tiny adjustment. A minor inconvenience considering what I have.

Item 2: Got it on the buffering. Wouldn't try to do that with the CO2 running.

Item 3: Got it on the ph range you suggest. Just trying to pick a happy medium amongst fish and plants.

Item 4: Some of this leaves me puzzled about something. Why turn off the CO2 when you know the PH will rise to it's buffered point? I thought the whole idea was to maintain a consistent ph range. Why would I intentionally need to induce a ph change?


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## rickey (Jul 7, 2013)

rpadgett37 said:


> Why would I intentionally need to induce a ph change?


The pH will fall at night when the plants aren't using CO2, so you aren't trying to induce a ph change but maintain a steady pH by not injecting at night

R


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## amphirion (Jan 15, 2014)

Plants do not photosynthesize in the dark. You will suffocate everything in there.


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## amphirion (Jan 15, 2014)

Fish are also incredibly resilent to change. The trick is to allow them to adapt to the change. With my CO2 system, I turn it on from 7-12, then 1-8. This allows the system to recharge (co2 degasses during the down time) preventing fish from suffocating and prevents algae from gaining foot.


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## rpadgett37 (Jan 1, 2014)

Oh my. I am very glad I asked that question. Now that you say it, it's pretty obvious but I completely missed it.

Thanks very much for setting me straight on that point. That would have been ugly.


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## rpadgett37 (Jan 1, 2014)

I have another question. I read in one of my test kits where KH "X" ppm has an excellent buffer capacity. What does that mean? 

In the instance of adding CO2 to a system, after which KH and PH will drop, does that mean the KH level will hold the PH in place, keeping it from fluctuating when the CO2 is introduced?


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## amphirion (Jan 15, 2014)

i hope you like chem.

KH = carbonate hardness, meaning, the presence of HCO3- and CO3-2 ions in the water. usually a result from calcium carbonate though sodium carbonate (baking soda) can do this also. when a chemical is said to have excellent buffer capacity, it means that it has an extraordinary means to resist change in the pH scale, despite large amounts of acid or base added to it.

pH can be deduced, rather than acidity and alkalinity, as the concentration of H ions found in a solution. the higher the concentration, the lower the p value. this is important to understand how buffers work.

when you are adding an acid into a system that is rich in carbonates or a high KH, you are adding H+ molecules. the following reaction occurs:

H+ + CO3-2 -> HCO3- 
did you see what happened there? a free proton ended up binding to a carbonate ion. I added in a proton into the water, but it was neutralized...the natural amount of H concentration remains the same, therefore the pH remains the same. as long as CO3-2 is in the system, almost every single H+ will be bound and the pH will change very slowly.

But wait! there's more!
What happens when all the CO3-2's have been used up? What if now we only have HCO3-? Then adding H+ will start altering the pH, causing it to become more acidic. And the pH will start dropping like a rock for a bit. But here's what makes carbonate such an excellent buffer:

H+ + HCO3- -> H2CO3

CO3-2 can accept another proton, thus neutralizing any proton added into the solution again, and pH measurements will show that the solution is resistant to change again.

TLDR: excellent buffer because it has two ranges where it is resistant to change whether to H+ or OH-.

When CO2 is added into the game:

CO2+ H2O <--> H2CO3 
H2CO3 <--> H+ + HCO3-
HCO3- <--> H+ + CO3-2
net reaction: CO2+ H2O <-> 2H+ + CO3-2 (this is what causes the pH to drop)

if your buffers lock the 2H+ (because of the first reaction), your CO2 remains CO3-2, preventing your plants from absorbing most of the CO2 that should be available to it.


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## rpadgett37 (Jan 1, 2014)

amphirion said:


> i hope you like chem.
> 
> KH = carbonate hardness, meaning, the presence of HCO3- and CO3-2 ions in the water. usually a result from calcium carbonate though sodium carbonate (baking soda) can do this also. when a chemical is said to have excellent buffer capacity, it means that it has an extraordinary means to resist change in the pH scale, despite large amounts of acid or base added to it.
> 
> ...


quote=amphirion;3761969]i hope you like chem.

OK. I am going to regurgitate what I am reading here. I failed Chemistry in College twice so bear with me.

Without CO2:

Water initially contains a balanced PH value where: 
H+ + HCCO3-2 = HCO3-

When H+ + HCO3-2 > HCO3- , then PH Drops until H+ + HCO3-2 = HCO3- once again (is that right?). 

In english, the more acid buffer I introduce (H+), the less PH is buffered (Higher concentrations of HCO3-2 to bond with the H+)

Does that also mean:

When H+ + HCO3-2 < HCO3-, then PH rises (Higher concentrations of HCO3-2 in the water for H+ to bond with) until H+ + HCO3-2 = HCO3- stabilizing PH once more (at a higher Ph value) 

In english, the less acid buffer (H+) I put in the water, the more buffered, the less the Ph value will change (it won't change very much).

Adding CO2:

So then in a setting where H+ + HCO3-2 = HCO3-:

Adding CO2 + H20 produces more HCO3- in the water, which will lower the Ph value until CO2 + H2O = HCO3-. 

In english, the more CO2 I add to the water, the higher the concentration of HCO3 produced, lowering the Ph until CO2 + H2O = HCO3- once more.

If there are more H+ ions in the water (more acid buffer), they will bond with both the HCO3- producing H2CO3- and CO3-2. With these and CO2 + H20 y7ou get CO2 + H2O <-> 2H+ + CO3-2 ???

Is HCO3 the type of carbon you want in the water for the plants? And it seems that some point all of the molecular reactions will balance until there is only the type of carbon you want in the water. Is that remainder what is measured by the CO2 ppm concentration?

In english, it seems that both the starting point of Ph and Kh and the ratio of one to the other has a significant impact on the CO2 ppm in the water. I am not sure where a good starting point is for introducing CO2. I want the water Ph at between 6.8 and 7 after CO2 infusion. My starting point is roughly Ph 7.1 with Kh at 60 ppm. It is buffered with both Acid and Alkaline buffers. At this point, is it a hit and miss with more or less CO2 in the system at this starting point until I reach the desired CO2 ppm?

Lots of meat here. I am sure I don't need to exactly know these specific details, but I want the frame of reference to understand what is happening in my tank.


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## amphirion (Jan 15, 2014)

put my explanations in orange



rpadgett37 said:


> Without CO2:
> 
> Water initially contains a balanced PH value where:
> H+ + HCCO3-2 = HCO3- *this equation is incorrect. HCCO3-2 is not part of the bicarbonate equilibrium, H2CO3, HCO3-, and CO3-2 are. if you meant H+ + HCO3- -> H2CO3, you would be correct*
> ...


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## rpadgett37 (Jan 1, 2014)

Yes. You've been very helpful indeed. For me, it's been a nice diversion from the incessant testing and adjusting of my water parameters. I do love a good puzzle.

All the same, setting aside the molecular interactions, I am taking out of it all:

1. Buffers stabilize the PH and KH in the water.
2. They inhibit fluctuations in these KH and PH , which to a degree is desirable. 
3. A higher buffer level will reduce the amount of usable Carbon Dioxide in the water for the plants.
4. Higher buffer level in KH means more CO2 must be added into the water to provide more usable CO2.
5. The ideal is to begin with a stable PH and KH that I want that will accommodate a downward movement of KH and PH , then add the CO2, adjusting it so that the ending CO2 puts these parameters into the zone I want overall in the aquarium.

That's the logic at least, and I understand adding plants will soak up CO2 which I am guessing will affect PH and KH once more, though I am not certain how that looks.

Also, the CO2 measurement in ppm, what exactly is that measuring? Is it the CO2 usable to the plants? Is it the total CO2 after the molecular interactions have occurred? Or is it just the CO2 total level independent of everything else?

Can you explain these last last parts for me?


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## amphirion (Jan 15, 2014)

CO2: parts per million. ex: CO2 is 30 ppm = for every million molecules, 30 of them are carbon dioxide, and is measuring exactly that. 

the third question is a little bit tricky because H2CO3 and H2O/CO2 dissociate freely at the equilibrium state where the creation rate is equal to the destructive state so they essentially cancel each other out. so generally speaking, yes it is taking into account those interactions. remember though, the rate at which products and reactants are formed depends on which side of the see-saw is heavier. the heavier it is, the longer it will take to reach equilibrium.

based on what we've discussed regarding buffers, acids, and bases, it is safe to say that CO2 is anything but independent of everything else, since it interacts with multiple molecules, including water.


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## rpadgett37 (Jan 1, 2014)

amphirion said:


> CO2: parts per million. ex: CO2 is 30 ppm = for every million molecules, 30 of them are carbon dioxide, and is measuring exactly that.
> 
> the third question is a little bit tricky because H2CO3 and H2O/CO2 dissociate freely at the equilibrium state where the creation rate is equal to the destructive state so they essentially cancel each other out. so generally speaking, yes it is taking into account those interactions. remember though, the rate at which products and reactants are formed depends on which side of the see-saw is heavier. the heavier it is, the longer it will take to reach equilibrium.
> 
> based on what we've discussed regarding buffers, acids, and bases, it is safe to say that CO2 is anything but independent of everything else, since it interacts with multiple molecules, including water.


True and that makes sense. I thought that was the case (last paragraph), but I wanted to be sure.

So in the end, there isn't any specific way to measure the amount of CO2 being used by the plants. It could be higher or lower in the ppm measurement depending upon what chemical reactions are actually occurring at any given time. 

I presume that an informed guess is all that can be manged based on a knowledge of what I have put into the water in terms of acid or alkaline buffers, a usable understanding of what interactions are occurring and a best guess as to whether there is likely more or less usable CO2 in the tank based on the assumed interactions. I'm afraid I lost my electron microscope in one of my many moves across the country so a guess is really all I can manage 

I wonder though if even a best guess is going to help much. Is it even noticeable, meaning can you narrow it down even further by simply observing the plants to see how they are doing? Can you gauge in this way if they are or are not getting enough usable CO2 from the water? OR is this area happening at a level so miniscule that you miss it if you sneeze?


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## amphirion (Jan 15, 2014)

yep. definitely. it's called "pearling" --the gas produced by the plants is indeed oxygen, a biproduct that indicates the plant is absorbing optimal amounts of CO2.









photo taken from here: http://www.aquaticplantcentral.com/forumapc/new-planted-aquariums/38583-my-plants-pearling.html

with regards to CO2 and plants, it is really a matter of statistics. what are the chances that a CO2 molecule found in the water makes contact with the surface of a leaf and be absorbed for photosynthesis. the higher amount of CO2 released into the water column will result in a higher amount getting absorbed into the plant, while a lower amount might not even get absorbed by the plant and be degassed from the water. obviously, you could let the CO2 run on full blast and your plants will definitely be absorbing CO2 by the droves, but your poor fish will end up suffocating (well, maybe not bettas).


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## rpadgett37 (Jan 1, 2014)

Oh my. That's wonderful.

I can't thank you enough for your assistance here. I can't say that I understand the chemistry all that well, but I can say that as I watch what is happening in the water in terms of KH / PH, I have a good picture of what interactions are taking place and what to expect as it happens.

Very useful stuff


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## amphirion (Jan 15, 2014)

The feeling is mutual. I'm glad you were able to learn something-- definitely not an easy topic to comprehend. Thanks for giving me the chance to get my nerd on (not really many instances where buffers and bicarbonates get to be brought up in casual conversation)


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