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Dialling in the CO2 injection Rate and CO2 Profiles

KirstyF

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25 Jul 2021
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Kidderminster
Can you post your full profile results from gas on to lights off? Might help folks to give some advice specific to your situation. 😊
 

Yugang

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13 Mar 2021
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Hong Kong
To find a tank’s CO2 level or baseline before injection starts, take a clean glass of tank water and leave it at room temp for 24 hrs after which take a pH reading. This will be the baseline or degassed pH of your tank water.
@Zeus. , although above is perfectly valid, I have another suggestion for an edit that may make life for the CO2 beginner a little easier.

Rather than having your aquarium water outgas for 24 hours, you may fill a jar with 10% aquarium water. Go outdoor, where ambient CO2 is predictable, open the jar lid and let fresh air in. Then shake violently, for the water to degas into the trapped fresh air in the jar. Open lid another 2-3 times, each time shake, and we're all set. I have my degassed reading within a minute, rather than 24 hours.

1653445143950.png
 

Hanuman

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Thailand
@Zeus. , although above is perfectly valid, I have another suggestion for an edit that may make life for the CO2 beginner a little easier.

Rather than having your aquarium water outgas for 24 hours, you may fill a jar with 10% aquarium water. Go outdoor, where ambient CO2 is predictable, open the jar lid and let fresh air in. Then shake violently, for the water to degas into the trapped fresh air in the jar. Open lid another 2-3 times, each time shake, and we're all set. I have my degassed reading within a minute, rather than 24 hours.

View attachment 189095

I am not convinced you can fully degass water that fast and bring it to equilibrium with a few shakes, but since I am no one I’ll let the pro scientist confirm this.


Sent from my iPhone using Tapatalk
 

Yugang

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Hong Kong
I am not convinced you can fully degass water that fast and bring it to equilibrium with a few shakes, but since I am no one I’ll let the pro scientist confirm this.


Sent from my iPhone using Tapatalk
You have a point, perhaps for some it takes one or two minutes more :lol:
Easy to verify making multiple measurements and see of pH rises further with more shaking.

shake violently
That's what I mean, assuming a more experienced UKAPS CO2 degasser. :lol:

1653451048810.png
 
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Sacul

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Joined
10 Dec 2020
Messages
64
Location
Devon
Thanks again guys, I'll do another degas and pH profile. I know what my previous degas values were so I'll try the shake method aswel and see if I can get the same results. Like you say I can always shake it a few more times for verification
 

JacksonL

Member
Joined
27 May 2015
Messages
121
@Zeus. , although above is perfectly valid, I have another suggestion for an edit that may make life for the CO2 beginner a little easier.

Rather than having your aquarium water outgas for 24 hours, you may fill a jar with 10% aquarium water. Go outdoor, where ambient CO2 is predictable, open the jar lid and let fresh air in. Then shake violently, for the water to degas into the trapped fresh air in the jar. Open lid another 2-3 times, each time shake, and we're all set. I have my degassed reading within a minute, rather than 24 hours.

View attachment 189095
I have been experimenting with this, I have found 3.5 minutes of shaking is what it takes to get my water to read the same pH as a 60 hour degas (which is what I have found it takes my water to fully degas)
 

Zeus.

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Yorkshire,UK
@Zeus. , although above is perfectly valid, I have another suggestion for an edit that may make life for the CO2 beginner a little easier.

Rather than having your aquarium water outgas for 24 hours, you may fill a jar with 10% aquarium water. Go outdoor, where ambient CO2 is predictable, open the jar lid and let fresh air in. Then shake violently, for the water to degas into the trapped fresh air in the jar. Open lid another 2-3 times, each time shake, and we're all set. I have my degassed reading within a minute, rather than 24 hours.

View attachment 189095

@X3NiTH ( aka ' The Half Blooded Prince) did a great post on it, I didn't add details about it as I was trying to get it as brief as possible. When I get time (or if someone provides a link to his thread/post) I will add a link to bottom of post. His post is more valid as he is our resident chemist after all ;)
 

Yugang

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Hong Kong
@X3NiTH ( aka ' The Half Blooded Prince) did a great post on it, I didn't add details about it as I was trying to get it as brief as possible. When I get time (or if someone provides a link to his thread/post) I will add a link to bottom of post. His post is more valid as he is our resident chemist after all ;)

I believe I found the post you mention, maybe there are more detailed posts from @X3NiTH but couldn't find
There’s a quicker way to do this and that’s to draw the sample and put it in a lidded container and shake the bejeezus out of it for a couple minutes or so and periodically exposing the sample to ambient air, you can then test the pH with a pH Pen or a dip strip.

I have been experimenting with this, I have found 3.5 minutes of shaking is what it takes to get my water to read the same pH as a 60 hour degas (which is what I have found it takes my water to fully degas)
This is a good start thank you @JacksonL :)
Of course details matter for having the maximum efficiency - just a little water in the jar not too much, open lid in fresh air regularly, and shake the hell out of it.
I shake out 0.5-1 pH in a minute, and of course the efficiency decreases as the water gets closer to the full ambient equilibrium state. By taking multiple measurements between shakes, one gets a good feeling if any more shaking is further increasing the pH or not.

Perhaps I may go a little off topic here, sharing some of my gut feel / intuition about CO2 gas exchange. One of my favorite professors, many years ago, taught me to always try and do estimations for having a feel for a complex system, before doing complex computation, as it is better to be approximately right than to be precisely wrong. So the below is nothing scientific, but at least for me helpful to understand what I am trying to do.

In steady state, my reactor injects about 5 bubbles per second. I took pictures of the reactor, and I count approximately 50 bubbles chaotically moving around in flow. Bubbles are typically 3-5 mm diameter, both injected as well as in the pupulation of 50.
As we have steady state, injecting 5 bubbles per second, we may assume also 5 bubbles disappear per second. If 5 bubbles disappear from a population of 50, this means that the average lifetime of a 3-5 mm diameter bubble is as short as 10 seconds ...
This estimation ignores a lot of physics and statistics going on in the reactor, is not accurate and not scientific at all. My key takeaway is that gas exchange of pure CO2 to pure water is remarkably fast.

I am also experimenting with my CO2 Spray Bar . This is a half pipe with 1 inch diameter, where gas can exchange at the open interface between CO2 and aquarium water. I have not yet done precise measurement, but when I turn off CO2 injection I see the half pipe already 50% empty in about 15 minutes. Again, how remarkably fast is CO2 exchange with water.

So why does it take 24 hours, or even longer to degas aquarium water in a jar standing outside? When above two examples show how fast gas exchange can be? This is probably related to transport phenomena in the steady water in the jar, absence of flow and turbulence. I am just guessing here. But I am not surprised that violently shaking up the jar, each time in fresh air, does speed up the process a lot.
 
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JacksonL

Member
Joined
27 May 2015
Messages
121
I believe I found the post you mention, maybe there are more detailed posts from @X3NiTH but couldn't find



This is a good start thank you @JacksonL :)
Of course details matter for having the maximum efficiency - just a little water in the jar not too much, open lid in fresh air regularly, and shake the hell out of it.
I shake out 0.5-1 pH in a minute, and of course the efficiency decreases as the water gets closer to the full ambient equilibrium state. By taking multiple measurements between shakes, one gets a good feeling if any more shaking is further increasing the pH or not.

Perhaps I may go a little off topic here, sharing some of my gut feel / intuition about CO2 gas exchange. One of my favorite professors, many years ago, taught me to always try and do estimations for having a feel for a complex system, before doing complex computation, as it is better to be approximately right than to be precisely wrong. So the below is nothing scientific, but at least for me helpful to understand what I am trying to do.

In steady state, my reactor injects about 5 bubbles per second. I took pictures of the reactor, and I count approximately 50 bubbles chaotically moving around in flow. Bubbles are typically 3-5 mm diameter, both injected as well as in the pupulation of 50.
As we have steady state, injecting 5 bubbles per second, we may assume also 5 bubbles disappear per second. If 5 bubbles disappear from a population of 50, this means that the average lifetime of a 3-5 mm diameter bubble is as short as 10 seconds ...
This estimation ignores a lot of physics and statistics going on in the reactor, is not accurate and not scientific at all. My key takeaway is that gas exchange of pure CO2 to pure water is remarkably fast.

I am also experimenting with my CO2 Spray Bar . This is a half pipe with 1 inch diameter, where gas can exchange at the open interface between CO2 and aquarium water. I have not yet done precise measurement, but when I turn off CO2 injection I see the half pipe already 50% empty in about 15 minutes. Again, how remarkably fast is CO2 exchange with water.

So why does it take 24 hours, or even longer to degas aquarium water in a jar standing outside? When above two examples show how fast gas exchange can be? This is probably related to transport phenomena in the steady water in the jar, absence of flow and turbulence. I am just guessing here. But I am not surprised that violently shaking up the jar, each time in fresh air, does speed up the process a lot.
As far as details go, I use one of the small test vials that come with Salifert NO3 tests. Half fill it, lid on and shake for a minute, then open it up for a few seconds, then repeat, then repeat again except the last shake goes for 1.5 minutes. I then leave it open for a bit to settle, no defined time, I generally do whatever needs doing on the tank, cut off older leaves, trim plants, check equipment etc.
I had been trialling it with 1 minute/2minute/3minute and 4 minute shaken containers, testing them, then at the same time taking a sample and letting it sit for 3 days. 3.5 minutes seems the sweet spot for my tank, but I assume there may be differences between tanks depending on water chemistry.
 

Sacul

Member
Joined
10 Dec 2020
Messages
64
Location
Devon
Can you post your full profile results from gas on to lights off? Might help folks to give some advice specific to your situation. 😊
After doing a new pH profile yesterday my drop seems to have gone back to stable. Not sure what happened on that odd day where it was out with the last reading being 7.16. I did the degas jar shake which made my degassed pH value higher than my 24hr sat glass of water.
24hr glass 8.23
Jar shake 8.32
At lights on I was at 7.34 and lights off 7.29.
Although it seems like I'm getting the 1ph drop, my drop checker still isn't lime green. It's still more of a darker green. Is this a problem or not really?
 

Hanuman

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Joined
4 Jan 2019
Messages
1,358
Location
Thailand
@Yugang This shaking thing was discussed here too by CEG4048.
 

Yugang

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Joined
13 Mar 2021
Messages
326
Location
Hong Kong
@Yugang This shaking thing was discussed here too by CEG4048.
It is a very logical method to speed up outgassing, but @ceg4048 being a resident of Chicago I had expected a more localised approach at 300 rpm

1653630008137.jpeg
 
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