# Can CO2 micro bubbles cause incorrect drop checker readings?



## xZaiox (2 May 2022)

Hi guys,

I've googled this multiple times before, and feel that the answers given are usually too vague. Do CO2 micro bubbles alter the drop checker reading? I.e could a perfectly normal CO2 level cause a yellow drop checker by the bubbles rising up directly into the checker? Or conversely could an inadequate level of CO2 give a lime green reading? The bubbles are concentrated CO2 after all...

Would love some other opinions


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## bazz (2 May 2022)

Bubbles going straight up into a drop checker I would imagine will give a false reading, it's not a true picture as to the CO2 content of the water for the rest of the aquarium.
Cheers!


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## Garuf (2 May 2022)

Yes.


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## Zeus. (2 May 2022)

xZaiox said:


> could a perfectly normal CO2 level cause a yellow drop checker by the bubbles rising up directly into the checker?


Yes 100%, and if enough bubbles get in could easily have clear Drop Checker (DC). A DC is best placed where the bubbles are being jetted down by the flow of water - which is normally directly opposite the filter return.


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## MMonis (2 May 2022)

I came  across this piece of info from the 2hr aquarist website :


> Many hobbyists like using drop checkers but they are not a reliable method of determining CO2 levels. Drop checkers are dependent on gaseous exchange at the exact site where the drop checker is located - this in turn depends on the water flow and position of the drop checker, quality of testing regents and color interpretation.
> 
> 'Green' doesn't mean that one has good levels of CO2 in the tank. It just means that at that position, the drop checker is receiving some CO2. This result can also be skewed badly if it is in a position to capture CO2 bubbles that would otherwise be off gasses through surface water.
> 
> ...


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## Zeus. (2 May 2022)

MMonis said:


> I came  across this piece of info from the 2hr aquarist website :


Which is where a pH probe with the sensor on a lead comes in handy, as then you can move the sensor all around the tank to see any fluctuations in pH level


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## xZaiox (2 May 2022)

Thanks for the comments guys, this has been helpful to me.


Zeus. said:


> A DC is best placed where the bubbles are being jetted down by the flow of water - which is normally directly opposite the filter return.


Thanks for this Zeus, I'm going to move my drop checker there and see if the colour changes. Do you think it's safe to assume that a lime green to yellow drop checker accompanied with a 1.3-1.4 pH drop is likely 30+ ppm of CO2? I've spent so many hours reading up on optimising CO2 but it feels like an absolute minefield of information. It seems drop checkers aren't hugely accurate and the classic 1.0 pH drop makes an assumption that the degassed CO2 is 3ppm, where it could potentially be lower. 

I've pushed my pH drop to 1.7, and my fish don't go to the surface but do breathe too fast for my liking, they seem uncomfortable at that level. I'm having difficulty figuring out where to draw the line.


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## Andy Pierce (2 May 2022)

This at least is easy: dial back until your livestock behave unstressed.


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## aquanoobie (2 May 2022)

xZaiox said:


> It seems drop checkers aren't hugely accurate and the classic 1.0 pH drop makes an assumption that the degassed CO2 is 3ppm, where it could potentially be lower.


Hi @xZaiox 
Degassed water can have anything between 0.5 to 5 or 8 ppm of CO2. Therefore 1 pH drop can have 5 to 50 or 80 ppm of CO2. It's like rolling the dice.


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## Zeus. (2 May 2022)

xZaiox said:


> Do you think it's safe to assume that a lime green to yellow drop checker accompanied with a 1.3-1.4 pH drop is likely 30+ ppm of CO2?


No a 1.0pH drop is approx 30ppm.


xZaiox said:


> It seems drop checkers aren't hugely accurate


DC are accurate, but only slow the pH and relative [CO2] in the air space between the tank water and the DC solution. If CO2 bubbles get into the DC then DC solution will show a false pH/[CO2]. Which is why I would always advise doing a pH profile in combination to the DC colour change, plus watch livestock carefully.



xZaiox said:


> I've pushed my pH drop to 1.7


The biggest pH drop my livestock could handle was about 1.4pH and the DC was very light yellow to clear. I was also using CO2 reactors so there was no CO2 bubbles in tank



aquanoobie said:


> Hi @xZaiox
> Degassed water can have anything between 0.5 to 5 or 8 ppm of CO2. Therefore 1 pH drop can have 5 to 50 or 80 ppm of CO2. It's like rolling the dice.


I would disagree with that, as [CO2] in water will follow Henrys law, we have our tanks at a relative constant temp and the air pressure is relatively constant. The atmospheric [CO2] (although slowly increasing) is still relatively constant. So therefore once the water has fully degassed/gassed for the same temp and atmospheric pressure the [CO2] in water will be the same all around the planet which I think is approximately 4ppm at room temp (@dw1305 / @X3NiTH)


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## aquanoobie (2 May 2022)

Zeus. said:


> I would disagree with that, as [CO2] in water will follow Henrys law, we have our tanks at a relative constant temp and the air pressure is relatively constant. The atmospheric [CO2] (although slowly increasing) is still relatively constant. So therefore once the water has fully degassed/gassed for the same temp and atmospheric pressure the [CO2] in water will be the same all around the planet which I think is approximately 4ppm at room temp


Hi @Zeus.
I agree with everything you said if we were to keep our tanks outside, but some homes don't have much ventilation in hot seasons with air conditioning or in winter with heating. The CO2 value varies from ~400 to ~2500 ppm which will affect degassed equilibrium levels. Below is a picture of a CO2 meter on a table at the White House Correspondent's Dinner on April 30th 2022, two days ago. It reads 2 233 ppm of CO2 in the room. These levels are not unusual.






Next issue is the actual equilibrium. In Diana Walstad's book is a referenced scientific paper that says the equilibrium is 0.5 ppm of CO2 at the traditional ~400 ppm outside.


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## Zeus. (2 May 2022)

aquanoobie said:


> CO2 value varies from ~400 to ~2500 ppm which will affect degassed equilibrium levels


Agree


aquanoobie said:


> Below is a picture of a CO2 meter on a table at the White House Correspondent's Dinner on April 30th 2022, two days ago. It reads 2 233 ppm of CO2 in the room. These levels are not unusual.


any thing above 600ppm CO2 is unsuitable for humans over any length of time IMO. You need to open a window or turn up the heat exchange to acceptable levels



aquanoobie said:


> equilibrium is 0.5 ppm of CO2 at the traditional ~400 ppm outside.


Which it could be as I didn't check 😬


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## Yugang (3 May 2022)

Agree with all  comments above, but adding below a remark on CO2 'mist' - very fine, nearly invisible bubbles that we get from some inline diffusors.

While a drop checker can be easily understood for a static situation with fully dissolved CO2 in aquarium water, it is far less obvious when changes over time happen, or when CO2 bubbles of various sizes are present (visible bubbles / mist).

As already said in previous posts, CO2 bubbles entering the bulb checker is a no-no, so the placement of the checker is important. But where it gets more complicated is when we  have really tiny bubbles from a diffusor, creating a mist.

I would argue that it is hard to quantify what CO2 mist  does with life stock, with plants, or with a drop checker. It will depend on many variables, so there is no simple answer. Imagine these little pure CO2 reservoirs hitting the gills of a fish, or plant leaf, potentially with significant impact compared to x ppm dissolved CO2

When there is ‘CO2 mist’ in the tank, I would not blindly trust any measurement (drop checker, pH probe or other CO2 probe), and rather focus on life stock signs of wellbeing and plant health. I find similar statements on several fora.


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## Simon Cole (3 May 2022)

Then there is the factor that any mist will collect on the under-side of leaves where stomata are abundant.
Milli-bubbles - 1 mm to 1μm
Micro-bubbles - 10 μm to 50 μm
Nano-bubbles < 200 nm
Seems odd that these classes do not overlap, but then I do make the rules up. 
Stomatal pores could be between 30 μm and 150 μm in diameter. Stomatal density could be between 30 and 300 per mm-squared. Sorry this is vague, but it varies from species to species and adaptation to submersion. 
I am guessing that milli-bubbles get trapped in the stomatal opening. Nano-bubbles and some micro-bubbles can probably enter the mesophyll freely. Drop checkers can probably trap and collect all three bubble classes.

I am sure that the concentration of dissolved carbon dioxide is important, but perhaps the gas bubbles are also very useful to living plant tissue. I guess that if you wanted to get accurate drop checker results for fully dissolved carbon dioxide, then you would need to remove the bubbles, and that this could potentially be degassing your "diffused" carbon dioxide in the same process. It makes me wonder how feasible it is to measure dissolved carbon dioxide levels without using the pH drop technique. Moreover, whether you use a drop checker or a pH drop, I wonder whether the dissolved carbon dioxide concentration would matter that much if bubbles are effective nutrient transporters anyway. Overall the drop checker is just a visual index and the pH drop is a measure of dissolved carbon dioxide potential. Some logic would apply if you used a grade of fine filter paper over your drop checker matching the size of the average stomatal opening, like Whatman grade 4; but you could alternatively go for something finer like Whatman grade 5; so why not use several filtered drop checkers so that you know the impact of gas bubble size if you were interested. Also, it is likely that fish gills trap or absorb carbon dioxide gas bubbles, so this is also relevant. 

My own view is that 'pearling' is also very useful to observe. Anecdotal evidence regarding visual cues like drop checkers are still very useful. Most of this is fairly paradoxical, but if I had to pick, I would say do all three because gas bubbles matter.   



Zeus. said:


> any thing above 600ppm CO2 is unsuitable for humans over any length of time IMO


  Cheers for this post. I am getting swollen feet (and far worse symptoms) and I am convinced that I am close to 4,000 ppm sometimes, so I'll ask my doctor for a kit because they are coming around soon.


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## Zeus. (3 May 2022)

Simon Cole said:


> Cheers for this post. I am getting swollen feet (and far worse symptoms) and I am convinced that I am close to 4,000 ppm


TBH I was unaware myself till I googled it last night. But ventilation in dwellings is so important to our well being esp with increasing energy cost. Planning on fitting a ventilated heat exchange/recovery system on present house as I remove all the drafts and trickle vents.


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## dw1305 (3 May 2022)

Hi all, 


Zeus. said:


> the atmospheric [CO2] (although slowly increasing) is still relatively constant. So therefore once the water has fully degassed/gassed for the same temp and atmospheric pressure the [CO2] in water will be the same all around the planet which I think is approximately 4ppm at room temp (@dw1305 / @X3NiTH)


We never found where the 3 ppm figure <"actually came from">. I had a look at the lab CO2 monitor earlier today and it was 562 ppm CO2.

cheers Darrel


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## aquanoobie (3 May 2022)

dw1305 said:


> 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 ), 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.
> 
> ...


Hi @dw1305 
This is enlightening, thank you! What would it take to make you curious enough to calculate 2500 ppm CO2?


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## dw1305 (3 May 2022)

Hi all,


aquanoobie said:


> What would it take to make you curious enough to calculate 2500 ppm CO2?


Strange you should mention that, but <"we have a thread">.

cheers Darrel


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## aquanoobie (3 May 2022)

dw1305 said:


> Hi all,
> 
> Strange you should mention that, but <"we have a thread">.
> 
> cheers Darrel


Hi @dw1305 
What I am looking for is how much in ppm CO2 is going to have degassed water at atmospheric 2500 ppm CO2. Sorry for the confusion.


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## dw1305 (3 May 2022)

Hi all,


aquanoobie said:


> Hi @dw1305
> What I am looking for is how much in ppm CO2 is going to have degassed water at atmospheric 2500 ppm CO2. Sorry for the confusion.


I can <"work that out">.

Cheers Darrel


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## xZaiox (3 May 2022)

Zeus. said:


> The biggest pH drop my livestock could handle was about 1.4pH and the DC was very light yellow to clear. I was also using CO2 reactors so there was no CO2 bubbles in tank


Zeus, can I ask what symptoms your livestock displayed when the CO2 was too high? I'm wanting to be extra vigilant and know what signs to look out for. I've read reports from people before who have claimed their only symptom was fish death, which is a worrying thought to me! I'm also confused how I was able to drop the pH 1.7 in the first place, from everything I have read, this sounds like in theory it should be a substantial overdose. As I was raising it, I kept thinking "surely they're going to head to the surface soon?".

Also thanks again to all those who have commented


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## Zeus. (4 May 2022)

xZaiox said:


> Zeus, can I ask what symptoms your livestock displayed when the CO2 was too high?


In my no fish 50l tank when the surface skimmer got blocked due to poor maintenance as forgot to clean it before going on holiday and scum was on the surface the high [CO2] caused the snails headed to the surface, plus lost some/most RCS in tank 
In my 500l tank with a 1.4pH drop DC nearly clear some fish (Harlequin Rasbora )would be at the surface when lights first came on, then they would be fine unless I fed them, feeding them would get the fish to dart about for food (as they do) and the extra effort would cause the Harlequin Rasbora to pass out and go belly up for a short while, they recovered pretty quick. After that I would only feed the fish after CO2 had gone off and all was fine. Surface agitation was excellent in the 500l. I did get the 1.4pH drop in less than 30mins which may have caused some species of fish to go to the surface on pH drop for a short while whilst they adjusted.
Many of the fish I still have some 6 years plus on, tank no longer has CO2 injection as we have moved Olympus is calling


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## xZaiox (4 May 2022)

Zeus. said:


> In my no fish 50l tank when the surface skimmer got blocked due to poor maintenance as forgot to clean it before going on holiday and scum was on the surface the high [CO2] caused the snails headed to the surface, plus lost some/most RCS in tank
> In my 500l tank with a 1.4pH drop DC nearly clear some fish (Harlequin Rasbora )would be at the surface when lights first came on, then they would be fine unless I fed them, feeding them would get the fish to dart about for food (as they do) and the extra effort would cause the Harlequin Rasbora to pass out and go belly up for a short while, they recovered pretty quick. After that I would only feed the fish after CO2 had gone off and all was fine. Surface agitation was excellent in the 500l. I did get the 1.4pH drop in less than 30mins which may have caused some species of fish to go to the surface on pH drop for a short while whilst they adjusted.
> Many of the fish I still have some 6 years plus on, tank no longer has CO2 injection as we have moved Olympus is calling


This is useful info to me, cheers


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## dw1305 (5 May 2022)

Hi all, 


aquanoobie said:


> how much in ppm CO2 is going to have degassed water at atmospheric 2500 ppm CO2.





dw1305 said:


> I can work that out.


<"[CO2] = P/KH = 3.87 x 10-4 atm/29.41 atm M-1 = 1.32 x 10-5 M"> which gives you <"3.74 ppm CO2"> when you substitute "3.87 x 10-4" with "2.5 x 10-3".

cheers Darrel


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## Simon Cole (5 May 2022)

What a pity. I hoped it would be higher.


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## MichaelJ (5 May 2022)

dw1305 said:


> Hi all,
> 
> 
> <"[CO2] = P/KH = 3.87 x 10-4 atm/29.41 atm M-1 = 1.32 x 10-5 M"> which gives you <"3.74 ppm CO2"> when you substitute "3.87 x 10-4" with "2.5 x 10-3".
> ...



Math looks good, but I am still at a loss why this was brought up... ?  Yeah, well... 2500 ppm of CO2. 

Cheers,
Michael


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## Yugang (5 May 2022)

Simon Cole said:


> What a pity. I hoped it would be higher.


Well, what's in a number if probably 80% of us (including myself), quoting a measured CO2 ppm number in tank water, may be as much as 20-50% off? **

It is pragmatic to prioritise day-to-day reproducible CO2, and stability over time during intra day photoperiod. Observe plants and lifestock, adjust slowly - whatever one _*believes*_ ppm is.

** My personal estimation based on all assumptions, uncertainties and errors involved in the measurement and calculation process. If anyone thinks this is too pessimistic, please do consider sharing your experience and write an article on best practices for CO2 aquarium measurement, with evaluation of chemistry and physics involved and proposed measurement technique


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## dw1305 (5 May 2022)

Hi all,


Yugang said:


> Well, what's in a number if probably 80% of us (including myself), quoting a measured CO2 ppm number in tank water, may be as much as 20-50% off? **


I agree, all of these numbers are based on the flimsiest of foundations.

cheers Darrel


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## MichaelJ (5 May 2022)

Zeus. said:


> In my 500l tank with a 1.4pH drop DC nearly clear some fish (Harlequin Rasbora )would be at the surface when lights first came on, then they would be fine unless I fed them, feeding them would get the fish to dart about for food (as they do) and the extra effort would cause the Harlequin Rasbora to pass out and go belly up for a short while, they recovered pretty quick


Ouch that's terrible... I assume this was due to accidentally pumping in way too much CO2 with faulty equipments or incorrect adjustments or so...  That would always keep me up at night if I would do CO2... I know it's a lot safer these days compared to how it used to be, but still.       

Cheers,
Michael


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## John q (5 May 2022)

Simon Cole said:


> Then there is the factor that any mist will collect on the under-side of leaves where stomata are abundant.


OK I need educating. Most scientific research suggests submerged aquatic plants don't have stomata, or if they do they aren't very efficient.  Maybe I'm reading the "Wrong" research? Any help pointing me in the right direction would be appreciated 🙏


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## Simon Cole (6 May 2022)

John q said:


> Most scientific research suggests submerged aquatic plants don't have stomata, or if they do they aren't very efficient. Maybe I'm reading the "Wrong" research? Any help pointing me in the right direction would be appreciated


Many true aquatic plants do not have stomata and use ectohydric surface capillary structures to obtain carbon dioxide through a process called laminar boundary layer conductance, which is a measure of diffusion. Some floating aquatic plants evolved non-functional permanently open stomata, and some simply exhibit a "loss of function" that could still allow them to adapt and close during periods of environmental stress. Pteridophytes which include ferns like _Bolbitis, _mosses, and certain liverworts, evolved a kidney-shaped (reniform) graminoid stomata, many of which stay open and retain the ability to close in dryer conditions. Marchantialean liverworts like _Riccardia _evolved without them, using special pores for photosynthetic gas exchange on the under sides of their leaves, and with humid air chambers beneath the cuticle. The role of air chambers is to enable endohydrotic conductance and this is thought to enhanced gaseous exchange and strike a balance between hydroscopic (wet) and hygroscopic (damp) environmental conditions (Vascular Transport in Plants, pages 69-89); there are also suggestions that some plants form similar air spaces (aerenchyma) as an adaptation to when they have been flooded. Generally speaking, plants that did evolve stomata, did so on the under side of leaves (hypostomatous), on both sides (amphistomatous), or on the top (epistomatous) to favour their own ecological niche.

However, plants that evolved "true" stomata, probably did so in more hydrodynamic conditions, and they make up the bulk of "immersed" aquarium stem plants that people are usually interested in enriching. When we see "pearling" we are probably observing very fast degassing, and it is likely that plants have opened their stomata to facilitate a rapid gaseous exchange. Flooding-induced stomatal closure is common in many terrestrial plants but nobody really knows how this happens. If certain immersed aquarium plants respond in the same way, then the question is, do they open back up again. And another question on my mind is, when they are closed, how big is the actual gap, and does this facilitate access of carbon dioxide bubbles into the intercellular spaces behind the guard cells; nano-bubbles are < 200 nm, so they only need a small gap to enter. For each plant species it is going to be slightly different and will depend upon varying environmental factors, but there have been suggestions that stomata in most species will open back up again when the osmotic conditions are suitable. It would be great if we knew the mechanism or if immersed aquarium species were studied independently, but for the time being this is simply a guess.

It is probably untrue to assume that stomata reduce in prevalence on immersed aquarium plants as an adaptation. They may close and be less recurrent in new growth, but there is not conclusive evidence that they disappear. Arabidopsis (stomatal initiation) is the process that governs whether the leaf meristemoid mother cell differentiates into either a pavement cell (standard epidermal) or a stomatal guard cell. It governs the stomatal abundance of a leaf (e.g. the stomatal index), and this is confined by the “one cell spacing” rule, and many other factors such as light intensity, gaseous exchange and temperature play an important role in stomatal abundance. We know that many C3 plants will often increase stomatal abundance when there are lower carbon dioxide levels and  this seems to be a long-term evolutionary trait, but there is also species specific variation. Whether this process is affected by immersed growing conditions is also likely to be species specific.

If stomata are open, then both hypostomatous and amphistomatous leaves will have a potential for capturing carbon dioxide bubbles of all sizes as well as dissolved carbon dioxide. That would imply that pH measurement and ppm approximations might not really be the target of investigation. Instead, "pearling" may be a far more accurate way to measure photosynthesis, not least because it is a measure of the effect of enrichment, as others have pointed out above. Plants that do this are good indicators that conditions are right. Plus it is best not to eliminate the role of aqueous pores and other gateways that probably provide a route for carbon dioxide bubbles to enter directly. After all, carbon dioxide diffusivity is about 10,000 times higher in air than in water, so if it is present in bubbles inside plant tissue (intercellular gaps) or sitting as a bubble in the stomatal opening, then the rate of diffusion into chloroplasts will be far faster. The rate of diffusion of an ionic solute or carbon dioxide molecules is inverse to the distance. It is a bit like standing next to the speaker in a punk rock concert, compared to hearing the faint rumble of a rave going on several miles away!


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## John q (6 May 2022)

Thanks for the detailed reply @Simon Cole  very much appreciated.


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## bazz (6 May 2022)

Simon Cole said:


> Many true aquatic plants do not have stomata and use ectohydric (surface capillary structures) to obtain carbon dioxide through a process called laminar boundary layer conductance, which is a measure of diffusion. Some floating aquatic plants evolved non-functional permanently open stomata, and some simply exhibit a "loss of function" that could still allow them to adapt and close during periods of environmental stress. Pteridophytes which include ferns like _Bolbitis, _mosses, and certain liverworts, evolved a kidney-shaped (reniform) graminoid stomata, many of which stay open and retain the ability to close in dryer conditions. Marchantialean liverworts like _Riccardia _evolved without them, using special pores for photosynthetic gas exchange on the under sides of their leaves, and with humid air chambers beneath the cuticle. The role of air chambers is to enable endohydrotic conductance and this is thought to enhanced gaseous exchange and strike a balance between hydroscopic (wet) and hygrophytic (damp) environmental conditions (Vascular Transport in Plants, pages 69-89); there are also suggestions that some plants form similar air spaces (aerenchyma) as an adaptation to when they have been flooded. Generally speaking, plants that did evolve stomata, did so on the under side of leaves (hypostomatous), on both sides (amphistomatous), or on the top (epistomatous) to favour their own ecological niche.
> 
> However, plants that evolved "true" stomata, probably did so in more hydrodynamic conditions, and they make up the bulk of "immersed" aquarium stem plants that people are usually interested in enriching. When we see "pearling" we are probably observing very fast degassing, and it is likely that plants have opened their stomata to facilitate a rapid gaseous exchange. Flooding-induced stomatal closure is common in many terrestrial plants but nobody really knows how this happens. If certain immersed aquarium plants respond in the same way, then the question is, do they open back up again. And another question on my mind is, when they are closed, how big is the actual gap, and does this facilitate access of carbon dioxide bubbles into the intercellular spaces behind the guard cells; nano-bubbles are < 200 nm, so they only need a small gap to enter. For each plant species it is going to be slightly different and will depend upon varying environmental factors, but there have been suggestions that stomata in most species will open back up again when the osmotic conditions are suitable. It would be great if we knew the mechanism or if immersed aquarium species were studied independently, but for the time being this is simply a guess.
> 
> ...


I'm glad you're on UKAPS!


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## dw1305 (6 May 2022)

Hi all,


John q said:


> Most scientific research suggests submerged aquatic plants don't have stomata, or if they do they aren't very efficient.


What @Simon Cole  says.  Evolution, via <"natural selection">, is <"pretty efficient"> at finding the <"optimal solution"> ("optimal" depends a little bit <"where you start from">).

From <"What's the general consensus on a back up heater?">.


> This is a cross-section through <"the floating leaf of a _Potamogeton_ sp"> (it is floating because you can see that there are stomata only in the upper (adaxial) leaf surface).







cheers Darrel


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## sparkyweasel (6 May 2022)

It may be relevant that many of our aquarium plants live submerged only seasonally in their natural habitat.


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## Simon Cole (7 May 2022)

Other thoughts on incorrect drop checker readings:
Bubbles adhere very quickly to glass. Depending upon the type of drop checker you choose, this can have an impact on measurement. As more bubbles combine against the glass surface, their buoyancy overcomes surface tension and they float upwards into the drop checker. This provides a sort of motorway express lane from aquarium water into the drop checker. Drop checkers can be categorised as having wide or narrow openings. In an ideal world, the gas pocket would be as small as possible, there would be minimal opportunity for bubbles to collect, adhere, and move up the glass into this airspace, and the interface between aquarium water and the gas pocket would be maximised. I have used both types and feel that they are both useful, but I am guessing that the narrow ones are better. Let me explain why:


< note how this "wide" drop checker has potential to capture more carbon dioxide bubbles through glass-adhesion mechanism because more aquarium water is in contact with the glass inside the cone, and also how the wide opening functions to captures bubbles.


 < this "narrow" drop checker is a bit more ideal. The meniscus is convex and will deflect bubbles away from the opening. Minimal bubbles can adhere to the glass and travel inside. There is lots of indicator fluid, and a smaller gas pocket than if the opening was widened. Had this been suctioned onto the glass nearer to the plants, then it would be comparatively more effective, but assuming that flow-dispersion is not a major factor, then it is hard to fault.

Bubbles can flatten. Silanized glass is hydrophobic, and bubbles can flatten against it when they adhere (shown below), and this process takes a matter of milliseconds depending upon the concentration of solutes, molecules that coat them, and a few other factors; the appearance is often a glimmering sheen. If drop checkers use regular glass, I suspect that any adhering bubbles are more rounded but still have strong adhesive forces, a tendency to combine, and buoyancy sending then upwards.  I do not have strong opinions favouring either glass type. Here is a milli-bubble adhering to silanized glass over 2 milliseconds:



As a side note, I think that the bubble flattening effect is more important if it happens on plant leaves. The morphology of plant leaves varies a lot from species to species, but they are not perfectly flat surfaces. I couldn't find any SEM images of aquarium plants to show you. I would presume that bubbles contacting leaves may either adhere to, get trapped, flatten, or provide a sheen over the leaf epidermis. This indicates that the size of bubbles is possibly very important, especially without open stomata, but apologies this is very off topic.


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## Yugang (7 May 2022)

Simon Cole said:


> Other thoughts on incorrect drop checker readings:
> Bubbles adhere very quickly to glass. Depending upon the type of drop checker you choose, this can have an impact on measurement. As more bubbles combine against the glass surface, their buoyancy overcomes surface tension and they float upwards into the drop checker. This provides a sort of motorway express lane from aquarium water into the drop checker. Drop checkers can be categorised as having wide or narrow openings. In an ideal world, the gas pocket would be as small as possible, there would be minimal opportunity for bubbles to collect, adhere, and move up the glass into this airspace, and the interface between aquarium water and the gas pocket would be maximised. I have used both types and feel that they are both useful, but I am guessing that the narrow ones are better. Let me explain why:
> View attachment 188094< note how this "wide" drop checker has potential to capture more carbon dioxide bubbles through glass-adhesion mechanism because more aquarium water is in contact with the glass inside the cone, and also how the wide opening functions to captures bubbles.
> View attachment 188095 < this "narrow" drop checker is a bit more ideal. The meniscus is convex and will deflect bubbles away from the opening. Minimal bubbles can adhere to the glass and travel inside. There is lots of indicator fluid, and a smaller gas pocket than if the opening was widened. Had this been suctioned onto the glass nearer to the plants, then it would be comparatively more effective, but assuming that flow-dispersion is not a major factor, then it is hard to fault.
> ...



I find it hard to quantify, and you may be right with your preference for the narrow dropchecker.

We could also make a case for a 'wide' drop checker, as it has a larger surface area between aquarium water and the pocket of gas, allowing a faster gas exchange and perhaps sooner equilibrium in the checker fluid.

A too narrow (approaching zero) checker certainly won't work, as there is no gas exchange at all. Perhaps there is somewhere an optimum between 'narow' and 'wide'.

I used both types simultaneously, and eventhough I was not interested in a full investigation I believe my results showed indeed a faster response of the 'wide' type.



Yugang said:


> While a drop checker can be easily understood for a static situation with fully dissolved CO2 in aquarium water, it is far less obvious when changes over time happen, or when CO2 bubbles of various sizes are present (visible bubbles / mist).


I have not done the math, but quantitatively understanding the workings in a non-static / not-fully-dissolved situation can become very tricky indeed as there are multiple processes of diffusion/outgassing /absorption/flow going on. For same reason it is hard to argue what is the best design. Just test one against the other is probably the best approach.


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## Simon Cole (7 May 2022)

Yugang said:


> Perhaps there is somewhere an optimum between 'narow' and 'wide'.


The solution I would like to see is a silicone membrane between the aquarium water and indicator solution interface, no air gap whatsoever.


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## Yugang (7 May 2022)

Simon Cole said:


> The solution I would like to see is a silicone membrane between the aquarium water and indicator solution interface, no air gap whatsoever.


Sounds good, almost a poor man's pH probe 

PS - Simon, I really enjoy your deep scientific insights, thank you for posting your thoughts.


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## Zeus. (7 May 2022)

MichaelJ said:


> Ouch that's terrible... I assume this was due to accidentally pumping in way too much CO2 with faulty equipments or incorrect adjustments or so... That would always keep me up at night if I would do CO2... I know it's a lot safer these days compared to how it used to be, but still.
> 
> Cheers,
> Michael


No accident or faulty equipment, Due to some CO2/flow related issues which I was trying to resolve by improving the CO2 supply to the plants, by going down the high[CO2] route which I would advise against with hindsight. When I took [CO2]  too high initially the fish was at the surface just after the pH drop, so a backed off a little and all was fine. However, if I fed the fish the Harlequin Rasbora/myself wasn’t happy with a  moment!!! they very quickly recovered , I didn’t feed them again till CO2 had gone off and it didn’t happen again. So it was the Harlequin Rasbora when being fed was the visual waring in tank that [CO2] was too high. Only had tank that high for a short while and never took the [CO2] any higher and never lost a fish in 500L tank due to high [CO2]. Once I got my Maxspect Gyres x2 and improved the tank flow/turnover I dialled back on the [CO2], which is the route I would advise if your [CO2] with 1.0pH drop isn’t doing what you had hoped, Increasing the tank turnover/flow helps remove/reduce the ‘dead spots’ and increase the supply of CO2 to your plants. Maxspect Gyres are great for the planted tank IMO/IME as you can have a timed schedule with different flow rates for each Gyre, high when CO2 is on variable speeds and low/off at night so clean up crew can do their job. In the words of our 'CO2 Guru' Clive ‘Flow is King in the CO2 enriched planted tank’ and many CO2 related issues are flow related issues

Only ever lost RCS in 50l (no fish in tank) due to forgetting to cleaning Ehiem skim before holiday 😢 it got clogged with detritus stopped skimming and returned home to the surface full of scrum.


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## Zeus. (7 May 2022)

Simon Cole said:


> The solution I would like to see is a silicone membrane between the aquarium water and indicator solution interface, no air gap whatsoever.


Which would remove the x10,000 slower diffusion rate in air  good thinking


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## Simon Cole (7 May 2022)

Zeus. said:


> x10,000 slower diffusion rate in air


The opposite way around, faster in air. I was thinking that this would mainly block bubbles but also eliminate the phase transitions.
On a side note, does anybody use carbon dioxide titration test kits?


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## Zeus. (7 May 2022)

Simon Cole said:


> The opposite way around, faster in air. I was thinking that this would eliminate the phase transitions.


,👍


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## xZaiox (7 May 2022)

Zeus. said:


> Once I got my Maxspect Gyres x2 and improved the tank flow/turnover I dialled back on the [CO2], which is the route I would advise if your [CO2] with 1.0pH drop isn’t doing what you had hoped


Zeus, what did you dial your CO2 back to? Do you now aim for a 1.0 drop or higher still? Did your plant growth take any hits from reducing the amount? I know you've improved the flow, but I'm curious if the plants that were previously in a good flow got effected by the reduction?


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## Zeus. (7 May 2022)

xZaiox said:


> Zeus, what did you dial your CO2 back to? Do you now aim for a 1.0 drop or higher still? Did your plant growth take any hits from reducing the amount? I know you've improved the flow, but I'm curious if the plants that were previously in a good flow got effected by the reduction?


I cant remember how much I dialled it back but the DC was light green, I think the pH drop was reduced to about 1.3pH. With having a duel stage reg duel Solenoid/needle values and reactors it was very simple I just reduced the working pressure as counting the BPS was a little pointless.

Once I had reduced the CO2 working pressure it took 30mins to get the target pH drop I was happy with at the time, before that it took 20mins. When checked the pH wasn't stable from lights on till CO2 off so instead off reducing the CO2 injection rate on that line, I added a little timed loop on my PLC so the CO2 injection was on for say 10mins then off for 30 seconds and fine tuned the on/off loop till it was stable. Having a PLC and a duel injection setup made getting a stable [CO2] very easy compared to a normal single timer/injection setup. 
The tank target [CO2] was well reduced in the Covid lockdown once my CO2 cylinders got low to very low levels as I could not get CO2. Reduced the lights and ferts at same time as well. Have since retired and moved and once moved the tank has been low tech since.

When I fitted the Gyres the plants just improved, it may of been lower [CO2] but the CO2 was delivered faster to the plants. Hygrophila pinnatifida never did well which i think was due to my very hard water.

The trouble with going for High [CO2] is when do you cut back if there's an improvement and how much do you cut back. Esp when you have a busy life at the time. It works so you continue. I would advise to always work on improving the flow once your at a lime green DC/1.0pH drop and your still having issues. Its just easier on most setups to dial the CO2 up a bit and improving the flow/turnover is harder, so we take the easy route as I did as my twin sparbar was maxed out




Plus ugly with pipework- which took 4-6hrs to clean.

My next high tech tank will be different again plan to use RO water, present house has a well so RO water will be relatively cheap compared to being on a meter where you pay per cubic meter twice once for supply the water and then for waste, which was one of the reasons I worked on the IFC remineralising sheet ( soon to be released). I do believe that remineralised RO water will enable me to achieve better results with some plants. I was never able to get Hygrophila pinnatifida to last more than 9 months with my hard water.
Think the vid below demonstrates the flow well

Getting good/great flow at substrate level in a three sided tank was the trick to the carpet which was over 50cm below water. It even had some MC in the carpet which got limited light and no elongated internodal stems the flow at the substrate level was so good.


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## xZaiox (8 May 2022)

Wow Zeus, what a beautiful tank, you've done a brilliant job! 😍 Excellent demonstration of good flow too - Some of my plants sway like that, but definitely not all of them. I'd like my monte carlo to grow better, and I'm assuming it's not getting enough flow being at the bottom of the tank. I had a look into that gyre pump you have, looks brilliant although quite costly. 

I've just recently ordered a spray bar for my filter - I've seen Clive's posts and it seems to work for him, so thought I'd give it a go. I'm hoping they don't clog easily like I'm imagining they probably do lol.


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## aquanoobie (9 May 2022)

aquanoobie said:


> Hi @dw1305
> What I am looking for is how much in ppm CO2 is going to have degassed water at atmospheric 2500 ppm CO2.





dw1305 said:


> Hi all,
> 
> 
> <"[CO2] = P/KH = 3.87 x 10-4 atm/29.41 atm M-1 = 1.32 x 10-5 M"> which gives you <"3.74 ppm CO2"> when you substitute "3.87 x 10-4" with "2.5 x 10-3".
> ...


Thank you @dw1305 very much for solving it. I was looking for this for some time and finally can see the light. So what is the result in terms of CO2 ppm at a given pH drop. We know from scientific papers and your calculations that atmospheric CO2 levels of ~400 ppm make water equilibrium of ~0.5 ppm. We also know that residential areas may have atmospheric CO2 as high as 2 500 ppm and thanks to you we now know what equilibrium this makes and that is 3.74 ppm. By having this data we can calculate tank CO2 ppm range of a typical pH drop,

1.6 pH, 19 - 150 ppm CO2
1.5 pH, 15 - 120 ppm CO2
1.4 pH, 12 - 95 ppm CO2
1.3 pH, 10 - 75 ppm CO2
1.2 pH, 8 - 60 ppm CO2
1.1 pH, 6 - 48 ppm CO2
1.0 pH, 5 - 38 ppm CO2

I don't know but these ranges, or inaccuracies, are posible and are dependent on the level of house ventilation function. Also this can explain why some people have success with 1.0 pH drop and others don't unless they go for larger drop.


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## dw1305 (10 May 2022)

Hi all, 


aquanoobie said:


> We also know that residential areas may have atmospheric CO2 as high as 2 500 ppm and thanks to you we now know what equilibrium this makes and that is 3.74 ppm. By having this data we can calculate tank CO2 ppm range of a typical pH drop,


I'm guessing that 600 ppm CO2 is a more realistic CO2 level for houses etc.  There are <"figures for the pH of Oceans"> under various atmospheric CO2 level scenarios. It is a lot easier for sea water, because it is pretty consistent world wide and fully saturated with dKH.   

cheers Darrel


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## sparkyweasel (10 May 2022)

I got a room CO2 monitor today. Only a cheap one so I don't know how accurate it is, but I think it will tell me the difference between a bit and lots, and whether it's increasing or stable. It also measures temperature and humidity, and those readings match those on another monitor I already have, so it may be reasonably OK.
It read 556ppm to start with. Then I sat in the room, breathing; went to 880ppm after 3 hours, flashing a yellow alert!
1205ppm after another hour and a half, orange alert!
I opened the window; dropped to 786ppm in an hour. Alert status; green. 
All very interesting, and needing further thought. 

EDIT; Two more hours with the window open and it's down to 527ppm.


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## sparkyweasel (10 May 2022)

dw1305 said:


> I'm guessing that 600 ppm CO2 is a more realistic CO2 level for houses





sparkyweasel said:


> It read 556ppm


Good guess.


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## aquanoobie (11 May 2022)

sparkyweasel said:


> I got a room CO2 monitor today. Only a cheap one so I don't know how accurate it is, but I think it will tell me the difference between a bit and lots, and whether it's increasing or stable. It also measures temperature and humidity, and those readings match those on another monitor I already have, so it may be reasonably OK.
> It read 556ppm to start with. Then I sat in the room, breathing; went to 880ppm after 3 hours, flashing a yellow alert!
> 1205ppm after another hour and a half, orange alert!
> I opened the window; dropped to 786ppm in an hour. Alert status; green.
> ...


Hi @sparkyweasel 
This is bombshell news in details thanks for sharing. What kind of CO2 monitor you got if I may ask.


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## aquanoobie (11 May 2022)

CO2 table


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## sparkyweasel (11 May 2022)

aquanoobie said:


> What kind of CO2 monitor you got if I may ask.


It's this one;
Meter
Lots of sellers have what looks to be the same one, some are a bit cheaper but slower to arrive. 
In fact mine was £12.55 but they have now put it up to £12.99, - I must be an influencer.


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## aquanoobie (11 May 2022)

sparkyweasel said:


> It's this one;
> Meter
> Lots of sellers have what looks to be the same one, some are a bit cheaper but slower to arrive.
> In fact mine was £12.55 but they have now put it up to £12.99, - I must be an influencer.


Funny, I didn't know they are so inexpensive, I must be living under a rock. So, what about a homework, can you find under water one in this price range?


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## sparkyweasel (12 May 2022)

aquanoobie said:


> can you find under water one in this price range?


I wish


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## Hanuman (12 May 2022)

sparkyweasel said:


> got a room CO2 monitor today. Only a cheap one so I don't know how accurate it is,





sparkyweasel said:


> It's this one;
> Meter
> Lots of sellers have what looks to be the same one, some are a bit cheaper but slower to arrive.
> In fact mine was £12.55 but they have now put it up to £12.99, - I must be an influencer.





aquanoobie said:


> Funny, I didn't know they are so inexpensive, I must be living under a rock. So, what about a homework, can you find under water one in this price range?


Be aware that those are not real CO2 detectors. They are actually extremely inaccurate and use a simple and cheap TVOC sensor which by design and specification are not meant to detect CO2 or measure in any way CO2 since they only output one signal. CO2 concentration is then extrapolated, calculated and faked through a chip. Proper CO2 detectors use what we call an NDIR CO2 sensors (nondispersive infrared sensor) which by themself are pricy. The component alone will cost ~30/40USD sometimes more depending the manufacturer. So any CO2 monitor out there retailing for less than 100/150USD or less will just be a scam and you can be warrantied that what you see on the screen of your cheap Chinese made device is no where close to the real concentration of CO2 in the air at any given time of measurement.


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## Simon Cole (12 May 2022)

@Hanuman  So a bit like that guy who made £50 million during the Iraq wars selling £13 novelty golf ball finders as bomb detectors to security forces worldwide at £27,000 each. You've got to pity Trading Standards somewhat.


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## Hanuman (12 May 2022)

Simon Cole said:


> @Hanuman  So a bit like that guy who made £50 million during the Iraq wars selling £13 novelty golf ball finders as bomb detectors to security forces worldwide at £27,000 each. You've got to pity Trading Standards somewhat.
> View attachment 188407


Thailand's Royal Army did purchase those at some point. I remember the scandal. The Army even tried BSing the public into believing this wass all legit and highly technologically advanced and people were too dumb to understand. It was brushed under the carpet following the backlash.
*edit*: typo


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## Hanuman (12 May 2022)

For anyone wanting to have a proper CO2 sensor, this is the cheapest I've found. It's a DIY kit that will require some soldering and a bit of coding skills, but nothing too extreme.





						The AirGradient DIY Kits
					

When we started to give away the AirGradient PCBs and only charged shipping costs, we got a lot of requests from builders about complete kits.




					www.airgradient.com
				




There are other CO2 DIY projects out there but you need to source the component yourself and the monitor will end up costing more. For example: https://www.the-diy-life.com/all-in...ality Monitor With CO2 Sensor - The DIY Life/
OR

You can go and buy a commercial CO2 sensor for the modicum price of 229USD 🙂








						Airthings Wave Plus | Smart radon and indoor air quality monitor
					

Smart, battery operated, indoor air quality monitor with 6 sensors: radon, CO2, humidity, temp, airborne chemicals (VOCs) and pressure.




					www.airthings.com
				



You will probably find cheaper ones but nothing that is genuinely a CO2 sensor for sub 100USD


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## aquanoobie (12 May 2022)

Hanuman said:


> Proper CO2 detectors use what we call an NDIR CO2 sensors (nondispersive infrared sensor) which by themself are pricy.


Hi @Hanuman 
Would this product qualify? 
It says, "With 2 different sensors: NDIR and TVOC provide 2 options for you, you can choose based on your requirement." And it costs CAD $36. 

Amazon product

It looks identical to what @sparkyweasel has.

3 IN 1 Portable LCD CO2 Meter Air Quality Carbon Dioxide Detector Tester Monitor  | eBay


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## Hanuman (12 May 2022)

aquanoobie said:


> Hi @Hanuman
> Would this product qualify?
> It says, "With 2 different sensors: NDIR and TVOC provide 2 options for you, you can choose based on your requirement." And it costs CAD $36.
> 
> ...



I'll be honest, I think that's a big fat lie. Considering the price it can only be a TVOC sensor. I wouldn't waste my money on that.


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## sparkyweasel (13 May 2022)

Hanuman said:


> NDIR CO2 sensors (nondispersive infrared sensor) which by themself are pricy. The component alone will cost ~30/40USD


When I considered building a meter, the sensors were about £10 to buy just one at retail price. I imagine the large-scale Chinese makers can get them a lot cheaper than that.
Even the kit you linked to has the option of with or without the sensor, and the price difference is only $20.


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## Hanuman (14 May 2022)

sparkyweasel said:


> When I considered building a meter, the sensors were about £10 to buy just one at retail price.


You see, el cheapo NDIR sensors like the one you just referred to are basically copies. Aliexperess is flooded by them. They are slow, inaccurate, unreliable. They usually have a detection range of 400-10000ppm or 0-5000ppm which technically is fine BUT with a very poor accuracy which can range from 100ppm to a 1000ppm 😬. There are not many companies producing quality NDIR. I suggest looking for Sensirion, Winsen, Cubic, Senseair. All produce quality, reliable sensors. Some are very expensive some very reasonable, but nothing like £10, that just wont happen and I wouldn't waste my money on those copies. 


sparkyweasel said:


> Even the kit you linked to has the option of with or without the sensor, and the price difference is only $20.





Hanuman said:


> The component alone will cost ~30/40USD sometimes more depending the manufacturer.


The Kit I posted earlier is the cheapest you will find with a good quality sensor. They use the Senseair S8 sensor which retails for 25/30USD depending where you buy it from. AirGradient is able to get it for slightly lower because they buy it by the hundreds.


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## Hanuman (22 Aug 2022)

Hanuman said:


> For anyone wanting to have a proper CO2 sensor, this is the cheapest I've found. It's a DIY kit that will require some soldering and a bit of coding skills, but nothing too extreme.
> 
> 
> 
> ...


I got myself this kit for 96USD. Got to say, seems pretty good. I added it in my bedroom last night before going to bed, and to no surprise the Co2 sky rocketed during sleeping hours. Maybe I should do something about this!!


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## dw1305 (22 Aug 2022)

Hi all,


Hanuman said:


> Maybe I should do something about this!!


I would, 2000ppm is <"getting towards the limit for healthy living">. It will definitely cause drowsiness, and above 2000ppm aerial CO2 you get


> ........ Headaches, sleepiness and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present.


Probably a silly question, but can you just open a window?

cheers Darrel


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## Hanuman (22 Aug 2022)

dw1305 said:


> Hi all,
> 
> I would, 2000ppm is <"getting towards the limit for healthy living">. It will definitely cause drowsiness and above 2000ppm aerial CO2 you get
> 
> ...


Yeah that won't be a good solution. Here in Thailand temps go in the 35-38C. We use air conditioning else it's just too hot to bear. But I definitely need to do something about this. Maybe ask my wife to sleep next room, although I anticipate that could be a cause for divorce. 😂


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## Hanuman (23 Aug 2022)

I barely opened the door and this is the result. Not ideal, but much better.


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