# Estimating CO2 injection rates in ml per minute



## ShawnMac (3 Aug 2016)

I'd like to request that members take a little time to estimate and post their CO2 injection rates in ml per minute. Many times we try to compare CO2 levels or injection rates using bubbles per second, which as many experienced hobbyists know, isn't that helpful. The bubbles are on different equipment and under varying operating pressures, which all impact the size of the bubbles. If we are able to start gathering some information on injection rates in ml per minute, diffusion methods, tank size, light levels, and plant mass; we might better be able to compare methods and help beginners find an injection rate with which to start based upon their specs. 

Of course this isn't a replacement for good horticulture like observing plant growth and other methods to estimate CO2 concentration (drop checker or ph/kh chart), but it could be another tool to help people get it right or trouble shoot problems. 

To estimate your injection rate use a graduated cylinder inverted over your diffuser, so that it captures the bubbles. Make sure the cylinder is full of water so that the CO2 can displace the water. In my case I had to use a small graduated cylinder and a small plastic funnel (all from my DIY ferts kit) to capture the bubbles and funnel them into the cylinder. After 60 seconds I measured 1.4 ml of CO2 gas trapped within the cylinder. It is best to do it this way for diffusers and atomizers since they are under some working pressure which effects the gas volume while still in the line or bubble counter. Removing the diffuser and putting the line straight in could change the injection rate to be measured. 

The method will have to be adapted for other injection methods like reactors by simply taking the line off the reactor and running into the measuring cylinder. While these systems are under some working pressure, it is much less than an atomizer...so hopefully there won't be a significant change to the bubble rate. 

I'll start:

45 cm aquascape with medium plant density (Iwagumi-ish) and high light. Moderate surface agitation, no skimming

Injection rate 1.4 ml/min through ADA pollen glass diffuser. 


Also, if you have any comments on the method please share them. I should add that this is not my idea, this was proposed by Tom Barr some years ago, however the method has never caught on. I hope we can change that.


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## zozo (4 Aug 2016)

How hard i try, what goes beyong my understanding what one would like to adchieve with this knowledge.. But besides that, I noticed in my case getting a very stable bubble count was near impossible. With a stop watch and my bad eye/hand coordination added. This probably is caused by the reducer/needle valve quality and age versus inveronmental temperatur or what ever other influence. I made the choice to invest in a ph controler istead of investing in a new reducer with the chance ending up with the same issue. At least with a ph controler i know a fluctuating bubble count aint such a big deal anymore.

I gues if you measure per minute one needs to be very sure that the bubble count is perfectly stable if not the estimate could be very far off at the end of the day with +/- the 600 minutes co2 is aded over the day.

But if i would like to know the ml/minute estimate i think monitoring the weightt of the botlle over a longer periode you could calculate back the average co2 use per minute a bit more precise.

What you need to know is the co2 volume/weight equivalents and los of weight from the bottle over x hours. Then it all comes down to the size of the bottle and quality of the weight scale you would use. Having a small co2 cardridge or a 500ml bottle a kitchen weightscale would do the job perfectly. 

I would like to assist you with your experiment, but since i use a 5 kilo FE i do not have the scale to pull it off. So i only can launch an idea how to get the estimate a bit more precise without fiddling around in your tank water. Maybe someone with a small soda stream cardridge gets curious and like to give it a go..


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## ian_m (5 Aug 2016)

Much better is gr of CO2 per hour per litre as much easier to measure, is completely independent of injection method and can be done without disrupting your carefully configured CO2 setup.

I use a set of Argos digital kitchen scales to weigh my FE at start of CO2 on time and at end of the day. I am using 15gr of CO2 in 8hours in 180litres with a green to yellow drop checker.

That works out 15/180/8 about 0.01gr per hour per litre.


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## Andy Thurston (5 Aug 2016)

ian_m said:


> Much better is gr of CO2 per hour per litre as much easier to measure, is completely independent of injection method and can be done without disrupting your carefully configured CO2 setup.
> 
> I use a set of Argos digital kitchen scales to weigh my FE at start of CO2 on time and at end of the day. I am using 15gr of CO2 in 8hours in 180litres with a green to yellow drop checker.
> 
> That works out 15/180/8 about 0.01gr per hour per litre.



What if you have a leak? how do you measure the co2 actually getting to your tank?


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## zozo (6 Aug 2016)

Andy Thurston said:


> What if you have a leak? how do you measure the co2 actually getting to your tank?



You shouldn't have one..  This is very easy to check, with a spray bottle filled with some water with dishwashing soap.. Spray it on every threaded connection and hosefitting. Even with the smallest leak you see little soap bubbles form.. This you should check everytime you even tough and move the bottle.. Just make sure you do not spray that stuff in your tank water and be carefull with the electrical part of the solenoid if you use one. Cover the solenoid with a dry cloth and only spray a tiny bit on the hose connector.


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## ian_m (6 Aug 2016)

Andy Thurston said:


> What if you have a leak? how do you measure the co2 actually getting to your tank?


If you have a leak, like I have had many times, then my consumption goes above 15gr a day. Easy peasy indication of a leak.


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## ShawnMac (8 Aug 2016)

Its nice to hear other methods. I think we can all agree that bps is not useful.


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## ian_m (9 Aug 2016)

Here is my grams per day consumption for my 14 FE's I have used. Spot where I had leaks....


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## Alexander Belchenko (9 Aug 2016)

Are you just weighing the cylinder?


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## ian_m (9 Aug 2016)

Alexander Belchenko said:


> Are you just weighing the cylinder?


Yes. Just plonk cylinder + regulator on scales at each water change. Write on cylinder the date and weight so can track how long the cylinder has left. Weight is about 5.7Kg for a new cylinder, dropping to 3.7Kg obviously when empty.


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## Daveslaney (9 Aug 2016)

ShawnMac said:


> Its nice to hear other methods. I think we can all agree that bps is not useful.


Who can honestly say they can tell the difference between 4 and 5 BPS? When i used a inline diffuser the BPS was uncountable.All it can give us is a ballpark figure really?


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## Franks (10 Aug 2016)

I can. 

Download an app to your phone called BPM. Then Tap away for every bubble you see for around 30 secs so a good mean BPM figure is established. Then simply devide by 60. 

See image:




Here you can see I tapped away for 144 bubbles which gives a bpm of 257. I convert the bpm in bubbles per second by deviding by 60 so 4.28bps 

Sounds more complicated than it is. 
I then log that figure with the time of day and pH of the water to plot pH drop.

Handy to do weekly once dialled in and also when swapping cylinders.

Sent from my E5823 using Tapatalk


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## roadmaster (10 Aug 2016)

ian_m said:


> Yes. Just plonk cylinder + regulator on scales at each water change. Write on cylinder the date and weight so can track how long the cylinder has left. Weight is about 5.7Kg for a new cylinder, dropping to 3.7Kg obviously when empty.



I like this, Much how I used to do to determine weight of large cichlid's I occasionally care/cared for to see what food's produced the most weight gain.
I simply took plastic specimen container and filled it to near  middle with water and weighed it.
Then insert the fish and weigh the specimen container again.
The difference was the weight of the fish.
Could track this over week's.


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## rebel (10 Aug 2016)

Daveslaney said:


> Who can honestly say they can tell the difference between 4 and 5 BPS? When i used a inline diffuser the BPS was uncountable.All it can give us is a ballpark figure really?



I use glycerine in the bubble counter which can slow the bubbles down a little.


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## roadmaster (10 Aug 2016)

roadmaster said:


> I like this, Much how I used to do to determine weight of large cichlid's I occasionally care/cared for to see what food's produced the most weight gain.
> I simply took plastic specimen container and filled it to near  middle with water and weighed it.
> Then insert the fish and weigh the specimen container again.
> The difference was the weight of the fish.
> Could track this over week's.



Hand's down, Hikari bio gold and chopped earthworm's produced best for me.


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## rebel (10 Aug 2016)

Has anyone tried to keep the cylinder on a set of scales constantly....Would this be ok to do? Would it affect the accuracy of the scales?


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## ShawnMac (10 Aug 2016)

Franks said:


> I can.
> 
> Download an app to your phone called BPM. Then Tap away for every bubble you see for around 30 secs so a good mean BPM figure is established. Then simply devide by 60.
> 
> ...


Even if you can, and I still doubt the accuracy of the taps. BPS is not useful because there is too much variation between systems. A more standardized method makes comparison better, although still not perfect.

The ph drop part is even more of a shot in the dark than the bubble tapping. Without knowing the kh value there is not an accurate way to estimate ph drop, it's just a wild guess.

sent from tapatalk on my phone so auto correct and other errors are bound to happen


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## ian_m (10 Aug 2016)

ShawnMac said:


> Without knowing the kh value there is not an accurate way to estimate ph drop, it's just a wild guess


You don't need to know your kH, pH drop is independent of kH, which is why you measure a change rather than an absolute value. Thus a 1 point drop in pH is about 30ppm CO2 regardless of your waters kH.


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## ShawnMac (10 Aug 2016)

KH acts as a buffer. The higher KH the more CO2 required to move the ph. It buffers the effect.

sent from tapatalk on my phone so auto correct and other errors are bound to happen


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## rebel (10 Aug 2016)

ShawnMac said:


> KH acts as a buffer. The higher KH the more CO2 required to move the ph. It buffers the effect.
> n


I think Ian means for the pH ranges that's common for aquariums, a 1 unit drop in pH roughly indicates about 30ppm of CO2 is around.


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## ShawnMac (10 Aug 2016)

rebel said:


> I think Ian means for the pH ranges that's common for aquariums, a 1 unit drop in pH roughly indicates about 30ppm of CO2 is around.


Still dependent upon the systems buffering capacity...injecting CO2 also consumes kh. 

We use 4 dkh in a drop checker for a reason. The indicator shows ph not ppm CO2, kh of the water impacts the ph reading. Same thing in our tanks

sent from tapatalk on my phone so auto correct and other errors are bound to happen


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## dw1305 (10 Aug 2016)

Hi all, 





ShawnMac said:


> We use 4 dkh in a drop checker for a reason. The indicator shows ph not ppm CO2, kh of the water impacts the ph reading. Same thing in our tanks


That is right, it is discussed in this thread <"Question about pressurised..">.

cheers Darrel


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## rebel (10 Aug 2016)

ShawnMac said:


> Still dependent upon the systems buffering capacity...injecting CO2 also consumes kh.
> 
> We use 4 dkh in a drop checker for a reason. The indicator shows ph not ppm CO2, kh of the water impacts the ph reading. Same thing in our tanks


Agree about the drop checker comment.

Agree about the buffering capacity.

Don't agree about injecting CO2 'consuming' kH. I don't it will meaningfully/practically change the kH at all.

Agree that pH drop will dependent on kH BUT for the ranges of pH,kH for our tanks, 1 pH drop is quite a reasonable starting point for about 30ppm of CO2.


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## ShawnMac (10 Aug 2016)

rebel said:


> Agree about the drop checker comment.
> 
> Agree about the buffering capacity.
> 
> ...




I agree, that it is a reasonable place from which to make an estimate. My point was that pH and KH are not in fact independent of each other. I cannot say what degree of pH change would be expected for a given amount of CO2 at a given KH and if that change is negligible within the average operating range of our tanks, it very well could be. I also don't remember quite enough of my stoichiometry to calculate it, it is possible to do though. I can say that my tank's KH fluctuates over time, due to the seiryu stone leaching carbonate. Goes from 7 dKH to about 14 dKH over 10 days. From memory, that alters the pH reading by about +0.3-0.4, which is enough to throw off our target...however an increase in buffering leads to an overdose not an under dose if using pH to set your target ppm. Water changes are our way of rectifying these fluctuations and maintaining normal ranges.

KH is "consumed", but like you mentioned it may be negligible. I cannot say. I still think it important to understand how the process works (the only times I really wish I'd remember more of my chemistry from college). I've used Seachem's great article as a good refresher. http://www.seachem.com/downloads/articles/General-Chemistry-of-the-Planted-Aquarium.pdf

All in all, estimating CO2 in our systems is an inexact science and we should accept some degree of inaccuracy while at the same time not over simplifying the relationships of the elements involved. We also can't lose the forest for the trees and should use our judgement and experience when targeting CO2.


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## Franks (10 Aug 2016)

ShawnMac said:


> Even if you can, and I still doubt the accuracy of the taps. BPS is not useful because there is too much variation between systems. A more standardized method makes comparison better, although still not perfect.
> 
> The ph drop part is even more of a shot in the dark than the bubble tapping. Without knowing the kh value there is not an accurate way to estimate ph drop, it's just a wild guess.
> 
> sent from tapatalk on my phone so auto correct and other errors are bound to happen


The accuracy of the taps becomes more tuned with the amount accounted for. If you only tap 6 times, the average will be poor. Tap 100 times accounting for every bubble will give you a super accurate indication of average. 

I also failed to indicate that this method is only for keeping an eye on your own setup or for when changing a canister etc, not for comparing bubble size with others. This is important when running larger tanks with a cranked needle valve.

Sent from my E5823 using Tapatalk


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## rebel (10 Aug 2016)

ShawnMac said:


> I agree, that it is a reasonable place from which to make an estimate. My point was that pH and KH are not in fact independent of each other. I cannot say what degree of pH change would be expected for a given amount of CO2 at a given KH and if that change is negligible within the average operating range of our tanks, it very well could be. I also don't remember quite enough of my stoichiometry to calculate it, it is possible to do though. I can say that my tank's KH fluctuates over time, due to the seiryu stone leaching carbonate. Goes from 7 dKH to about 14 dKH over 10 days. From memory, that alters the pH reading by about +0.3-0.4, which is enough to throw off our target...however an increase in buffering leads to an overdose not an under dose if using pH to set your target ppm. Water changes are our way of rectifying these fluctuations and maintaining normal ranges.
> 
> KH is "consumed", but like you mentioned it may be negligible. I cannot say. I still think it important to understand how the process works (the only times I really wish I'd remember more of my chemistry from college). I've used Seachem's great article as a good refresher. http://www.seachem.com/downloads/articles/General-Chemistry-of-the-Planted-Aquarium.pdf
> 
> All in all, estimating CO2 in our systems is an inexact science and we should accept some degree of inaccuracy while at the same time not over simplifying the relationships of the elements involved. We also can't lose the forest for the trees and should use our judgement and experience when targeting CO2.


Shawn you make good points.

It's important to remember that in the Co2 > Carbonic acid equilibrium, most of the CO2 remains in water as CO2(dissolved). Only 1:400 (I think) go to carbonic acid. Even less so to the right. So kH is not affected. This is my basic understanding. *This is missed by most beginners.*


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## dw1305 (10 Aug 2016)

Hi all, 





rebel said:


> So kH is not affected. This is my basic understanding. *This is missed by most beginners.*


That is right as well, there is some discussion is in <"Aquasoil pH increase..">.

cheers Darrel


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## zozo (11 Aug 2016)

I believe it was MarcelG who experimented a lot with this, he does some kind of horticultural study (never found out what his excact study is) and did al sort of lab tests on aquatic plants. He controversialy decided to go down with co2 to 15ppm and achieved equaly good results.. Anybody intrested find his posts, they are worth reading.. It doesn't answer the TS question, but it's more an answer to what and why and how much are you estimating and what for.
http://www.ukaps.org/forum/threads/...hing-to-alternatives.37923/page-5#post-410277


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## Manuel Arias (25 Aug 2016)

ian_m said:


> You don't need to know your kH, pH drop is independent of kH, which is why you measure a change rather than an absolute value. Thus a 1 point drop in pH is about 30ppm CO2 regardless of your waters kH.



Uh, not at all! This statement is quite misleading and totally wrong. Shawn is right: without kH information, drop into pH is just telling you that there is injection of CO2 but nothing else. And there is no reason to tell that 1 unit of dropping in pH is equal to 30ppm concentration. Different kH values will have different buffer effect, masking the effect of CO2 injection. It does not matter the pH ranges in which we are talking about; smaller jumps of pH at high kHs are just the result of large amounts of CO2. However, at low kH values, a bit of CO2 injection can cause a large drop of pH. The only situation in which Ian is correct is when the kH is equal to 4, that can be common in planted tanks, but not necessarily the case of most. Just check it in the table below, for example.



 

Cheers,
Manuel


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## Alexander Belchenko (25 Aug 2016)

I doubt you will ever got 120ppm CO2 @ 4 dKH when your pH is 6.


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## Manuel Arias (25 Aug 2016)

rebel said:


> It's important to remember that in the Co2 > Carbonic acid equilibrium, most of the CO2 remains in water as CO2(dissolved). Only 1:400 (I think) go to carbonic acid. Even less so to the right. So kH is not affected. This is my basic understanding. *This is missed by most beginners.*



Be careful, Rebel. This is only true in high-tech tanks, As Seachme says:

"In a planted aquarium employing a properly set up CO2 injection system the KH and pH should remain stable because one adds only as much CO2 as the plants need, thereby maintaining a constant level of CO2. In practice this is what you get when you use a CO2 injection system with a pH feedback metering system."

kH is *only preserved* when you inject as much CO2 as being consumed by the plants. Your statement is correct in high-tech tanks with lot of control, but will not work in low-tech tanks, when the plants will actually consume kH to obtain the inorganic carbon they need. From Seachem, again:

"In a well planted tank without CO2 injection the plants will use the CO2 available, causing the carbonates present to re equilibrate thereby producing more CO2. The acidifying agents mentioned above will also tend to drive the bicarbonate equilibrium to produce more CO2. In this type of setup the presence of acidifying agents can have a beneficial effect; it helps to maintain a higher level of CO2 than would be present if utilization were the only driving force for the formation of additional CO2. With this system one must actively maintain the KH by periodically adding bicarbonate based buffer. The plants are in essence 'eating' the buffer."

Besides, even at high-tech, people aim to get a stable concentration of CO2, which is not the same than adding the amounts plants are consuming as there is also a degasification process. The error here is to assume that losses of CO2 in the system, when injection CO2, are only due to plants consuming it, but this is not true. Degasification process will have also an effect into the CO2 concentrations. And in fact, by Henry's law, the higher the concentration water respect to the equilibrium point, the larger the degasification process will be, meaning that more CO2 is required to keep a stable concentration (i.e. CO2 injection should be equal to plant consumption + degasification). At high pH this is not much an issue, as inorganic carbon is mainly in bicarbonate form, but below pH=8.2 fraction of gas increases, and degasification will start. The lower the pH the larger the degasification will be. 

Nonetheless, kH will remain unchanged so far you cover the assumption of adding more than being used by the plants.


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## Manuel Arias (25 Aug 2016)

Alexander Belchenko said:


> I doubt you will ever got 120ppm CO2 @ 4 dKH when your pH is 6.



Make your numbers: http://www.chem1.com/acad/webtext/pdf/c3carb.pdf

You can doubt it but you are wrong. There are many information around showing similar results.

For instance: http://aquadaily.com/2009/01/29/co2-ph-kh-chart/

Or this one: http://aquariuminfo.org/co2calculator.html

Or this other reading, if you prefer: http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html

Obviously these are theoretical values, which are not considering, for example, the role of alkalinity (assuming all alkalinity is associated to carbonates). There can be some deviation between reality and these tables and results, but they are quite close to be useful.

Cheers,
Manuel


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## ian_m (25 Aug 2016)

Manuel Arias said:


> Uh, not at all! This statement is quite misleading and totally wrong. Shawn is right: without kH information, drop into pH is just telling you that there is injection of CO2 but nothing else. And there is no reason to tell that 1 unit of dropping in pH is equal to 30ppm concentration. Different kH values will have different buffer effect, masking the effect of CO2 injection. It does not matter the pH ranges in which we are talking about; smaller jumps of pH at high kHs are just the result of large amounts of CO2. However, at low kH values, a bit of CO2 injection can cause a large drop of pH. The only situation in which Ian is correct is when the kH is equal to 4, that can be common in planted tanks, but not necessarily the case of most. Just check it in the table below, for example.
> 
> 
> 
> ...


Sorry but one pH drop in tank water equates to approximately 30ppm regardless of dkH your chart confirms this. I say appoximate as there can often be interfering other chemicals affecting a pH reading, but for plant keeping is fine.

Normal tank water will have about 3ppm CO2 from the atmosphere. So for instance with a dkH 10 the pH at 3ppm will be 8. Drop the pH by one to 7 by injecting CO2 and you will find the ppm is now 30ppm. Same for 5dKH, pH is 7.7 drop to 6.7 and ppm is 29.9. If you had a table going higher than pH 8 you will find exactly the same is true, 30ppm corresponds to pH drop of 1. It is a physical chemistry fact going from 3ppm to 30ppm (changing by one unit of power of 10) will drop pH by 1.


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## Manuel Arias (25 Aug 2016)

ian_m said:


> Sorry but one pH drop in tank water equates to approximately 30ppm regardless of dkH your chart confirms this. I say appoximate as there can often be interfering other chemicals affecting a pH reading, but for plant keeping is fine.
> 
> Normal tank water will have about 3ppm CO2 from the atmosphere. So for instance with a dkH 10 the pH at 3ppm will be 8. Drop the pH by one to 7 by injecting CO2 and you will find the ppm is now 30ppm. Same for 5dKH, pH is 7.7 drop to 6.7 and ppm is 29.9. If you had a table going higher than pH 8 you will find exactly the same is true, 30ppm corresponds to pH drop of 1. It is a physical chemistry fact going from 3ppm to 30ppm (changing by one unit of power of 10) will drop pH by 1.



You are right, but only if we assume that the system reached equilibrium, i.e. your starting pH is equal to the one you get considering a pure bicarbonate solution at equilibrium with atmosphere. Plants and CO2 injection means that starting point in a running tank, everyday, is not necessarily that one, and dropping pH for one unit can mean higher concentration of CO2. In other words, if you have kH 4 and you have already 6ppm of CO2, a drop of pH in one unit leads you to 60 ppm. This is why I mean is misleading, because you assume your tank gets fully in equilibrium everyday and that is not necessarily the case.


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## Alexander Belchenko (25 Aug 2016)

The real problem with this chart: it assumes we can properly measure carbonate hardness aka KH. But all available KH tests on any market can't measure real KH. They all measure alcalinity.


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## Manuel Arias (25 Aug 2016)

Alexander Belchenko said:


> The real problem with this chart: it assumes we can properly measure carbonate hardness aka KH. But all available KH tests on any market can't measure real KH. They all measure alcalinity.



Having a problem reading kH does not invalidate the values in the chart, which was your original point. It just means that we cannot estimate with accuracy CO2 levels, whether you use a pH meter and looking for the 1 unit drop (which as I have pointed out, just works at certain circumstances) or you take your kH/pH measurements. Due to this is why using drop checkers is better, because they are not affected by other types of alkalinity, but then you have the issue of the color determination, but there are ways to improve that. The above chart links the color of the drop checker with the CO2 concentration. Indicator solution only changes color as a function of pH inside the drop checker, which usually comes in a solution with 4 dkH obtained by dissolving bicarbonates, i.e. no side effect of other substances into alkalinity, so it really works, so far you can determine the right color. However, it is enough for most people.

Cheers,
Manuel


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## Ed.Junior (23 Feb 2017)

ian_m said:


> Sorry but one pH drop in tank water equates to approximately 30ppm regardless of dkH your chart confirms this. Normal tank water will have about 3ppm CO2 from the atmosphere.



I am sorry for resurrecting an old thread but I really need help here.

I agree with the 10x progression, but where did you find this "3ppm CO2 from the atmosphere"?
I have been going through this over and over, and what I've found out is that our tanks should have around 0,55ppm of CO2 from the atmosphere.
I would love to be wrong and learn something...

I played around with Henry's Law, mostly with the solubility being defined via concentration, so that I can finally find it. That can be calculated using [CO2(aq)] = KH x pCO2

To calculate the CO2 partial pressure I considered that the air had 0,037% CO2 and temperature is 25C, and to be a bit precise, we discard the water vapour pressure by using this equation: pCO2 = (P° - pH2O) * XCO2
The result is:
pCO2 = (P° - pH2O) * XCO2
pCO2 = (1,0000 atm - 0,0313 atm) * 3,7 x 10-4
pCO2 = 3,69 x 10-4 atm

I dont think removing the water vapour is relevant, but I did anyways.
From there we proceed with the rest.

[CO2(aq)] = KH * pCO2
[CO2(aq)] = 3,38 x 10-2 * 3,69 x 10-4 mol x L-1 x atm-1 x atm
[CO2(aq)] = 1,25 x 10-5 mol x L-1

and then convert it to mg/l:

[CO2(aq)] = 1,25 x 10-5 * 44 x 103 mg x L-1
[CO2(aq)] = 0,55 mg x L-1

So, in the end I am looking at this 0,55ppm value and wondering, is that it, really?
A 1 point pH drop would add 5,5ppm. Considering that the water is not completely degassed from one day to the other, it would be possible to higher levels after a couple days.


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## Ed.Junior (23 Feb 2017)

You can find Henry's constant values at https://en.wikipedia.org/wiki/Henry's_law


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## dw1305 (23 Feb 2017)

Hi all,


Ed.Junior said:


> I played around with Henry's Law, mostly with the solubility being defined via concentration, so that I can finally find it. That can be calculated using [CO2(aq)] = KH x pCO2


I'm not a CO2 user, but I think you are right, the level of dissolved CO2 depends upon Henry's law, and if you assume 400 ppm CO2 in the atmosphere, standard pressure (1013mb) and a temperature of 20oC, then you have 1.35 x 10-5 mols l-1 of CO2 dissolved.

The RMM of CO2 is 12 + (16*2) = 44 (44g of CO2 in one Kg ), and if you work that out as ppm, it comes to ~0.6ppm (0.594ppm). The reason that that level is higher than the quoted 0.55ppm is just because the level of atmospheric CO2 has risen.

We have a CO2 monitor in the lab. and that usually sits at about 600ppm, but it is still along way from there to the dissolved 3 ppm quoted.

The only reference I could find for the 3ppm datum was the experimental work that George and Karla Booth did in the 1990's <"CO2 loss in large aquariums">.

cheers Darrel


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## xim (23 Feb 2017)

Every claim I've found about this seems to be from George and Karla Booth. All the links here are their writings.

http://www.hallman.org/plant/booth2.html
"After letting the water equilibrate for one day we measured dissolved CO2 at 2-3 ppm. We then set up a large powerhead to circulate the water (Project RS-500, ~500 gph) and let it run for a day. The CO2 remained about 2-3 ppm. At the end of most of the tests, CO2 again measured about 2-3 ppm, indicating that this was the equilibrium value for the experimental conditions (note that the altitude was 5000 feet above sea level)."


http://aquaticconcepts.thekrib.com/Co2/
"This is good for the fish. However, fish won't produce enough CO2 to raise the level above normal equilibrium levels (2-3 ppm) unless you are massively overcrowding the fish. It will diffuse into the air as fast as the fish produce it."


http://aquaticconcepts.thekrib.com/Co2/co2_faq.htm
CO2 has a natural equilibrium in water of about 0.5 mg/l. In an aquarium with a moderate fish load, the fish may raise the concentration to 2 to 3 mg/l.


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## zozo (23 Feb 2017)

If we assume CO2 is a simple gas we can apply Henry’s law but there seems to be more to it..! 
says..
http://www.thuisexperimenteren.nl/infopages/Carbondioxide in water equilibrium.doc
Above is a .doc version you need M$ word..  Google cache version click here.

According to this the atmospheric Carbon dioxide in water equilibrium is


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## AverageWhiteBloke (23 Feb 2017)

I'd like to add something to this conversation but I have nothing. Me, this discussion and my education parted company about seven post back.   However, problem I find with this level of accuracy and being dead on balls accurate (that's technical term for the scientists amongst you) is it's something that can never be replicated or a one size fits all result. A bit like E.I dosing the results might be right for your tank an nobody else's. Water temp, surface agitation, water chemistry,amount of plants, type of lights, reliability of co2 equipment, throughput of filter, dirty diffuser the list is endless and that's just in your tank so how would it relate to someone else's? If you found out a result today could you replicate it tomorrow? Maybe some water evaporated off in an open top tank and you have more surface agitation than you had yesterday, it's like herding cats, the possibilities are endless.

Coming back to the OP original question. Why can't we use those things we see in hospitals that measures the amount of gas going through a tube? That's something I've often wondered. Another thing I did one night while drinking a decent bottle of Merlot  and I'm probably going to wish I never said this...I had a bubble counter that was running too fast to count the bubbles so what I did was download an app for my phone that you could import in video and edit it. Then you could look at the video in the timeline at the bottom and play it back frame by frame and see how long it took in 1/10's of seconds per bubble. Obviously this won't tell you how much gas went in because of the size of the bubble but it can give you an idea of if you're fine tuning your own bubble count...I guess.

In my situation though it was never stable enough which was probably down to the quality of the regulator. Even whether the heating was on in the house seemed to make a difference.

BTW I was asked to "leave" school when I was 14 so I'm just glad I made it this far in the conversation


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## Ed.Junior (23 Feb 2017)

I guess the point for me is just understanding whats the level of co2 in water, when in equilibrium with the atmosphere. 

I do not need it to have good results, it was more of a curiosity. A 1 point pH drop works for a lot of people. For me I kind of need 1.4 to 1.5, to get optimal results.

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## AverageWhiteBloke (23 Feb 2017)

Yeah, for sure. I have an inquisitive mind as well. I'd like to know the results even if they are no use to me. I suspect one day they will. When I tried dropping my ph by one point I found there appeared to be a bit of a glass ceiling around .8 of a drop. Didn't seem to matter what I did it wouldn't go any lower.

My water comes out the tap at a PH of about 7.2, after the water change which pretty much re-set the gasses before co2 on my PH was about 7.0 and I took ph tests with a calibrated pen every half hour. At lights on I was at about 6.4 so I gave the needle valve an 1/8th of a turn and left it hoping to get some more results the next day and confirm the turn had worked.
The next day before the co2 was on and with a calibrated pen the ph was at 6.8 so I guess not all the co2 had gassed off from the previous day. By the time the lights came on I measured a ph of 6.2, the DC wasn't yellow and my Ember Tetras were showing signs of discomfort, hanging around in a group in the the top corner breathing heavy so I immediately dropped the water level and let the lilly pipe break the surface and turned the co2 back down an 1/8th of a turn.

I left it like that for a few week, DC was green at lights on, fish were happy and no signs of co2 related plant issues. Then the quandary starts with is it my ph pen, is it my calibration fluid, is it my DC fluid,is it me 

The moral of this story is the 1 drop in PH relates to 30ppm of dissolved co2, maybe I had it maybe I didn't. But someone forget to tell the fish and plants and they're the best judge of how much co2 should be in a tank IMO.


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## zozo (23 Feb 2017)

Ed.Junior said:


> A 1 point pH drop works for a lot of people.



0.5 pH drop can work as suficient, at least it does for me..  It kinda depends, i guess for the biggest part with the light intensity and plant sp. you are growing. I don't want to know the amount of co2 many people are wasting on their 30ppm or 1 unit pH drop goal. Without knowing  they could have same results with much less.


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## Ed.Junior (24 Feb 2017)

zozo said:


> I don't want to know the amount of co2 many people are wasting on their 30ppm or 1 unit pH drop goal. Without knowing  they could have same results with much less.



Well, while I understand your perspective, I come from the high tech side, and testing upper/lower requirements comes pretty soon.

I guess a lot of people could use less, specially when you have a very "relaxed" relationship with your tank.

For me, it is all about learning how it works and why it works. More light? Less light? More co2? Less ferts? More water changes? I'm trying lots of things so I can learn it.

I would be glad to use less CO2, but in my case it has to be there to keep up with 150+ PAR of light. You have to know your tank, understand its boundaries.







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## AverageWhiteBloke (24 Feb 2017)

Ed.Junior said:


> I would be glad to use less CO2, but in my case it has to be there to keep up with 150+ PAR of light. You have to know your tank, understand its boundaries.



I think there lies the problem. One person's experiment doesn't really relate to someone else's tank. It's quite overwhelming the amount of information available and everyone who frequents this forum are here for very different reasons. If I see a new comer in the forum one of the first things to ask is what are they trying to achieve. Some people here just want some plants growing, some are getting a scape put together ready for a photo shoot for competition, some just a community fish tank and other don't want any chemicals or gas and high lighting just want it as nature intended, the Walsted way.

To the unsuspecting new punter they might feel that they have to replicate the competition tanks habits to grow some plants and before long their pockets are empty and they are disillusioned with the hobby and worse not even enjoying something that should be an enjoyable experience. The 1 unit drop is more for the quick scaper and right on the edge for people with fish of being a disaster IMO. BTW that tank of yours is beautiful.  I can only dream. I can't see any fish in there though so I can only guess which side of the coin you are on.  Going off some of the chemical/mathematical hieroglyphics you posted earlier you're clearly a man of science.

I'm not being negative at all about this whole thing BTW. I'm following the post with interest because I will glean some useful information out of here and would like to see the results. I often find myself carrying out experiments just out of curiosity, the problem being when I do and let people know I often find that something else negates the results which I'd over looked but hey, it was fun while I was doing it.

My point was that if we all do the funnel thing capturing co2 we input and post our results what do we do with the answer? For instance right off the bat not all that co2 is going to end up in the container because some will dissolve in the water before it gets to the container so we have a duff result already. It's akin to finding out how long a piece of string actually is then realising we don't know what to do with the string or why we wanted a piece of string to start with.

I learnt my lesson from a shrimp tank on my desk. I would sit with test kits reading every post available. Stressing over every parameter and looking for answers, measuring this and measuring that. I've even seen myself nip home from work because I forgot to dose my macros in the morning.  The shrimp tank, I put some cat litter in from a previous set up, few cuttings from my home tank, some RCS and a couple of stones I found round my way and the pleasure I got out of it was immeasurable. Only dosing when it looked like it needed it and changed water when I had some spare time. 

The 1PH drop on a tank like yours is probably a must. On my desk shrimp tank not necessary and again, someone forgot to tell the plants because I was sick  of thinning them out.


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