# CO2 Diffusion and Drop Checker Setup



## LTPGuy (Aug 8, 2012)

Hi,

I've tried to grow plants for years and only recently did I stumbled across EI dosing, but more interestingly the Drop Checker. These two things sparkled a fire in me that has not stopped burning.

DROP CHECKER

I know how to use the drop checker (DC). I've made one, and recently purchased the glass bulb with the inverted funnel.

I've made my own 4dK solution and uses Nutrafin pH low range test solution. The 4dK solution was not tested or verified.

My observation with the DIY setup is as follow...
1. Colour does change from purple-blue to yellowish depending on the amount of CO2 injected. I know the target is lime green (30 ppm).
2. It takes a day or more for the colour to stabilized.
3. There is water flow under the opening of the drop checker.
4. The opening is 1" in diameter narrowed to 1/2" inside the checker. Picture below...

View attachment 21193
View attachment 21194


I have note that the purchased drop checker behaved similarly.

From what I have read, it should take about 1 to 2 hours for the colour to stabilized. I have the following question...
1. What is the proper ratio (volume to volume) of pH test solution to the 4dK solution?
2. Does the amount of pH test solution affect the rate in which the colour stabilized?
3. Does the total volume of the DC solution affect the rate?
4. Do I need to measure and perhaps make a new batch of 4dK solution?
5. Anyone else with similar obversation?

CO2 DIFFUSION

The second part is WRT to CO2 diffusion. I don't know if it should be posted on a different thread, but since they are related to the DC, I'll add it here and move it later if needs be.

I've tried various approach to CO2 diffusion from bubble into the filter intake, to venturi diffuser, to powerhead into an inverted bell, bubble ladder, airstone, etc.

I am currently using a setup similar to pumping water into an inverted bell.

With fresh tap water, the rate of dissolution is incredibly fast, 200mL of CO2 in less than a minute for 30G of water. This rate decreases (take longer to dissolve) as the CO2 concentration increases.

Note that this close to 100% dissolution. No CO2 were wasted via bubbles to the surface.

There will be a point when no more CO2 can be dissolved, or the dissolution rate is much lower than the amount of CO2 being injected, and the CO2 in the "bell" begins to accumulate and eventually overflow.

My observation are:
1. Fish all seems to be doing well. No gasping at the surface or heavy breathing. Healthy eating habit, and activities.
2. Plants are bubbling like crazy. Riccia can double in mass in a day or two.
3. The equilibrium rate of CO2 being inject is 1 bubble every 5-8 seconds.
4. Drop checker are showing lime green with a blue tint. Not yellow or yellow green.

My question are..
1. Is it safe to assume that the water column is saturated with CO2?
2. If yes to 1, this is insane as it would be 1450 ppm by mass. I know the ideal setting is 30 ppm.
3. Is my solution in the drop checker out of calibration or improperly made.

Also in my setup, the undissolved CO2 and/or air mixture under the bell is completely purge at a certain level so only CO2 are present at all time.

Any thoughts or comments or suggestions?

Thanks.


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## Darkblade48 (Jan 28, 2008)

LTPGuy said:


> I've made my own 4dK solution and uses Nutrafin pH low range test solution. The 4dK solution was not tested or verified.


How do you know the solution was properly made?



LTPGuy said:


> View attachment 21193
> View attachment 21194


Your photos do not work.



LTPGuy said:


> 1. What is the proper ratio (volume to volume) of pH test solution to the 4dK solution?


You can add as much bromothymol blue as you want to the solution so that the colour is easy to read. You should not add so much that it becomes opaque.



LTPGuy said:


> 2. Does the amount of pH test solution affect the rate in which the colour stabilized?


No.



LTPGuy said:


> 3. Does the total volume of the DC solution affect the rate?


Yes; the larger the volume, the more time it will take to absorb CO2, resulting in a longer time for the bromothymol blue to change colour.



LTPGuy said:


> 4. Do I need to measure and perhaps make a new batch of 4dK solution?


As previously mentioned, unless you know for sure it is 4 dkH reference solution, I would make a new batch.



LTPGuy said:


> My question are..
> 1. Is it safe to assume that the water column is saturated with CO2?


The water is not saturated with CO2.



LTPGuy said:


> 2. If yes to 1, this is insane as it would be 1450 ppm by mass. I know the ideal setting is 30 ppm.


How are you calculating this number?



LTPGuy said:


> 3. Is my solution in the drop checker out of calibration or improperly made.


See above.


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## LTPGuy (Aug 8, 2012)

*CO2 Concentration*

Thanks for your answers Darkblade. Google did not turn up the specific you had mentioned here.

I made the reference solution by making 40dK amount and then further dilute it down to 4dK purely by measured amount. All according to instruction I google.

I have a scale with 0.01g precision.

I don't have any test kit, so there is no way I can verify that the solution made were indeed 4dK.

When the solution was fresh, it appeared to be working as plants were doing well, and fishes were all "happy".

I think I will make a fresh batch. Do you have a recommendation for a test kit?

WRT to the CO2 concentration, the solubility of CO2 at STP is 1.45g per L. Even with gassing out due to surface tension and plants uptake, if the injected CO2 continues to overflow in the bell, I make the hypothesis that no more CO2 can be dissolved and hence the solution must be saturated.

Of course, the insane amount of O2 dissolve as most of the plants were gassing or pearling, could displace the amount CO2 thus changing it solubility.

Can you or anyone comment why no more CO2 can be dissolved. As I have indicated, when adding fresh dechlorinated tap water the dissolution rate is quite significant, so I believe the diffuser to be working very well.

Furthermore, the gas/CO2 inside the "bell" is purge completely near the overflow point so surface film, and less soluble gases are all purge leaving mostly CO2 inside the bell.

Here is the photo of the drop checkers currently in the setup.


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## Darkblade48 (Jan 28, 2008)

LTPGuy said:


> Thanks for your answers Darkblade. Google did not turn up the specific you had mentioned here.


Glad my chemistry minor could help. My specialist in microbiology never seems to have any practical usage other than grossing out people ("Did you know that you're probably eating 10^6 CFU of _Listeria_ *right now?*")



LTPGuy said:


> I made the reference solution by making 40dK amount and then further dilute it down to 4dK purely by measured amount. All according to instruction I google.


Not sure which instructions you used, but it should be OK. There could be differences in reagents etc. that may also affect your solution.

Ideally the dilution from 40 dKH to 4 dkH should be done with a volumetric flask, but a graduated cylinder will work in a pinch 



LTPGuy said:


> I have a scale with 0.01g precision.


This is fine depending on what you are weighing out, see above.



LTPGuy said:


> I think I will make a fresh batch. Do you have a recommendation for a test kit?


The API test kits are the ones that everyone seems to use; they work OK as long as they are new (check the batch date code printed on them).

There are better kH test kits, but they are much more expensive.



LTPGuy said:


> WRT to the CO2 concentration, the solubility of CO2 at STP is 1.45g per L. Even with gassing out due to surface tension and plants uptake, if the injected CO2 continues to overflow in the bell, I make the hypothesis that no more CO2 can be dissolved and hence the solution must be saturated.


You are making the assumption that the CO2 is already evenly dispersed throughout the entire aquarium, which is oversimplifying the scenario. You have to consider diffusion rate of CO2 (out of the aquarium), other gases that will lower CO2 Ks, also the fact that while the water surrounding the bell diffuser may be saturated, the far end of the aquarium may not be, etc.

Don't forget that if you were achieving that high of a CO2 concentration in your water, your fish would all be dead.


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## LTPGuy (Aug 8, 2012)

*Thanks*

Thanks again for your inputs. I'll come back to this post when make a new batch and verify the solution.

I am trying to build a CO2 diffuser that is as close to 100% efficient as possible.

I've seen the ceramic bubbler which appears to be wasting a lot of CO2 with bubbles not completely dissolve at the surface.

Other approach still appears to result in fine CO2 bubbles at the surface.

I know CO2 is cheap, but call it a hobby!


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