# Dissolving atmospheric CO2 into the water column



## minorhero (Mar 28, 2019)

I tried to dissolve atmospheric co2 in the water using a reactor. My results are questionable as the darn thing either clogged or didn't work properly. I am currently running into some annoying plumbing issues and unable to fix them without (likely) buying a new pump. However, I will say any attempt to dissolve room air into the water must be done without creating any bubbles in the aquarium otherwise the co2 we are trying to foster will outgass faster then we can put it into the water.

If you run a bubbler in an aquarium you will get the same levels of co2 you get from surface contact which ends up being around 1-4ppm of co2 depending on where you are at in the world.


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## Diana Walstad (Aug 17, 2019)

There is no way to substantially increase CO2 input from the air. Air containing only 0.04% CO2, is just a poor source of CO2, no matter what the temperature, pH, etc. 

Decomposition of organic matter--whether in the water or soil--plus fish respiration are the only realistic sources in a low-tech tank. Conserving CO2 is equally important. In aquariums, precious CO2 is frequently lost by excessive aeration and water/air churning.


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## [email protected] (May 22, 2019)

minorhero said:


> I tried to dissolve atmospheric co2 in the water using a reactor. My results are questionable as the darn thing either clogged or didn't work properly. I am currently running into some annoying plumbing issues and unable to fix them without (likely) buying a new pump. However, I will say any attempt to dissolve room air into the water must be done without creating any bubbles in the aquarium otherwise the co2 we are trying to foster will outgass faster then we can put it into the water.
> 
> If you run a bubbler in an aquarium you will get the same levels of co2 you get from surface contact which ends up being around 1-4ppm of co2 depending on where you are at in the world.


I don't think we can raise the content of CO2 in the water higher than the atmospheric pressure allows it without using pressurized CO2.

My question is how can we maintain the CO2 for instance around 4pmm or what ever the maximum natural ppm is. In my understanding, the air stone will help achieve the natural balance meaning, if there is less CO2 in the water then it should help dissolve it but if it's higher then it will help outgass it. So does surface agitation, those who inject CO2 don't want surface agitation where low tech actually need it. (some one correct me if I am wrong)


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## mboley (Jan 26, 2018)

Diana Walstad said:


> There is no way to substantially increase CO2 input from the air. Air containing only 0.04% CO2, is just a poor source of CO2, no matter what the temperature, pH, etc.
> 
> Decomposition of organic matter--whether in the water or soil--plus fish respiration are the only realistic sources in a low-tech tank. Conserving CO2 is equally important. In aquariums, precious CO2 is frequently lost by excessive aeration and water/air churning.


I have heard conflicting info on whether I need to have a surface turbulance in my low tech/Excel tank.

Right now I have a single output from my cannister with quite a bit of flow. As water level decreases, I do get an air water mixture until I replenish with make up water. Do I need to avoid that at all costs? How much surface turbulence should I have? None?

If you could please clarify. Thanks


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## minorhero (Mar 28, 2019)

Diana Walstad said:


> There is no way to substantially increase CO2 input from the air. Air containing only 0.04% CO2, is just a poor source of CO2, no matter what the temperature, pH, etc.


Unfortunately my experiment has shown this to be true from what limited data I was able to get from it when I know it was working. My idea was to find a way to get that .04% of co2 into the water repeatedly as some kind of cumulative effect. It did not work.

@[email protected] the 4ppm is kind of the max if you happen to live in a place that has 4ppm. It could just as easily be 1ppm. But chances are your aquarium already has some co2 in it that is greater then what mere atmospheric exchange would create. I tested my own aquarium water with a LaMotte test kit. It varied slightly depending on whether it was early in the morning or late in the evening but generally I had around 5ppm of co2 with pool filter sand substrate. This would just be from the breakdown of organic matter in my aquarium. So fish poop, plant leaves melting, wood slowly decomposing, etc.

@mboley there is more then one reason for wanting some surface agitation but not a lot. Yes if you have bubbles going everywhere you will definitely be out gassing co2. Excel is not however co2. Its a liquid form of carbon (or so I understand I could be very wrong about it but I believe it doesn't behave the same way as co2 when it comes to out gassing). The reason for some surface agitation concerns getting rid of the bacterial film that covers the surface of an aquarium. Its supposed to block atmospheric exchange which in many aquariums is the main source of new oxygen into the water. A surface skimmer or overflow is a better method of getting rid of this film. It may not be a better method for preserving co2 (actual co2 not excel) in our water.


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## Deanna (Feb 15, 2017)

Ahhhh ...in search of the Holy Grail. It's not worth trying to maximize atmospheric CO2. The most you'll ever see is ~3-4ppm and the difference is meaningless (consider that high tech tanks set 30ppm as a baseline). If you want to maintain a low-tech tank, you'll get the best enhancement by using products such as Excel. If you keep your light low-med in either (or both) terms of intensity and duration, you should be able to do quite well with lower-light plants. 

If/when you decide that you want more, the typical process is that we start by playing around with DIY CO2 approaches and then, after realizing how much of a pain it is and how the variability can disrupt the stability, we either move on to CO2 regulators or back down to the Excel again.


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## Desert Pupfish (May 6, 2019)

Deanna said:


> Ahhhh ...in search of the Holy Grail. It's not worth trying to maximize atmospheric CO2. The most you'll ever see is ~3-4ppm and the difference is meaningless (consider that high tech tanks set 30ppm as a baseline). If you want to maintain a low-tech tank, you'll get the best enhancement by using products such as Excel. If you keep your light low-med in either (or both) terms of intensity and duration, you should be able to do quite well with lower-light plants.
> 
> If/when you decide that you want more, the typical process is that we start by playing around with DIY CO2 approaches and then, after realizing how much of a pain it is and how the variability can disrupt the stability, we either move on to CO2 regulators or back down to the Excel again.


Dennis Wong on his website talks a lot about using tanks with lots of surface area, and low tanks so plants are closer to the surface and the light. Check out his section on growing carpet plants in a low tech tank--has lots of useful info on the size & depth of tanks, how a soil substrate helps, etc. I'm assuming you're wanting to maximize plant grown in a low tech tank--Dennis has lots of useful tips on how to accomplish this w/o injecting CO2.
https://www.advancedplantedtank.com/carpeting-plants.html


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## Edward (Apr 11, 2005)

[email protected] said:


> Hello everyone,
> In this thread I want to discuss the question of how dissolving atmospheric CO2 can be promoted in low tech aquariums.


 Very well, hook up an airstone.


> There is so much CO2 around us, how ca we help it get into the water?


 Obviously not enough CO2 out there. There used to be much more and plants are now suffering.


> How does temperature affect solubility of CO2 in water?


 Colder water can have more CO2, but fish don’t like it.


> How does PH affect solubility of CO2 in water?


 It doesn’t, unless we go lower than 3.65 – 4.00.


> What are other parameters that can affect achieving best solubility?


It is simply limited by the atmospheric CO2 levels, nothing we can change.


[email protected] said:


> So does surface agitation, those who inject CO2 don't want surface agitation where low tech actually need it. (some one correct me if I am wrong)


Yes wrong, we need oxygen for sure. 



Deanna said:


> Ahhhh ...in search of the Holy Grail. It's not worth trying to maximize atmospheric CO2. The most you'll ever see is ~3-4ppm and the difference is meaningless (consider that high tech tanks set 30ppm as a baseline).


 Yes, and even higher.



So, here you have it. If you still want to experiment maybe this here can help.


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## ursamajor (Oct 6, 2015)

Here's what affects the solubility of gas in water:

Pressure. The higher the pressure of a gas, the more it dissolves in water. As it happens we are increasing atmospheric CO2 levels. You just might have to wait a bit before you can appreciate the results in your tank.

Temperature. Gas is less soluble in warm water and more soluble in cold water. This is why cold water is more oxygen-rich.

Physical properties of the gas. Some gases are more or less soluble in water than others. This is one variable you can't tweak.

Under these constraints, a tank of room temperature water exposed to air reaches equilibrium at around 3-4ppm dissolved CO2, as previously mentioned. You can make your tank stay closer to this equilibrium by increasing the water-air interface available for dissolving gas. That's really all there is to it. It seems the most practical way to meaningfully raise CO2 is to expose the water in your tank to higher pressures of CO2, which is what bubbling pure CO2 into your tank does.

Higher CO2 levels can be found in nature, but nature follows the same rules. For example - living things in water produce metabolic CO2, raising the pressure of CO2 the water is exposed to, raising CO2 levels. A champagne bottle illustrates the same effect.


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## Diana Walstad (Aug 17, 2019)

[email protected] said:


> I don't think we can raise the content of CO2 in the water higher than the atmospheric pressure allows it without using pressurized CO2.
> 
> My question is how can we maintain the CO2 for instance around 4 pmm or what ever the maximum natural ppm is. In my understanding, the air stone will help achieve the natural balance meaning, if there is less CO2 in the water then it should help dissolve it but if it's higher then it will help outgas it. So does surface agitation, those who inject CO2 don't want surface agitation where low tech actually need it. (some one correct me if I am wrong)


The natural CO2 level is 0.5 ppm (amount of atmospheric CO2 that dissolves into water), not remotely close to 4 ppm. In a low-tech tank, vigorous agitation will only remove CO2 produced by decomposition. That's why I recommend very gentle water flow from a submerged pump. Currently for my small tanks (5-20 gal), I use no circulation at all or VERY gentle bubbling from a glass tube connected to an air-pump. The exception is the first few months of a low-tech tank with a soil underlayer, where there's a large reservoir of CO2 from the rapid decomposition of fresh soil organic matter.

For those that inject CO2, surface agitation just means that you have to increase the CO2 flow-rate to compensate. Many people with CO2 injection aren't aware of this and/or they don't care.


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## Edward (Apr 11, 2005)

Diana Walstad said:


> The natural CO2 level is 0.5 ppm (amount of atmospheric CO2 that dissolves into water), not remotely close to 4 ppm.


 Can you expand on that please?


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## Blue Ridge Reef (Feb 10, 2008)

mboley said:


> I have heard conflicting info on whether I need to have a surface turbulance in my low tech/Excel tank.
> 
> Right now I have a single output from my canister with quite a bit of flow. As water level decreases, I do get an air water mixture until I replenish with make up water. Do I need to avoid that at all costs? How much surface turbulence should I have? None?
> 
> If you could please clarify. Thanks


Excel is not truly liquid carbon. CO2 is not found at room temperature except under pressure as in our gas canisters. Excel contains glutaraldehyde. Tons of threads (some quite heated) on what it does and does not do available through the search feature of this forum. But to answer the simple part of your question, surface agitation will not affect how Excel works. You can do a 10x dose of Excel and it doesn't register on a drop checker (I've tried). So no CO2 *to* degas when using it -outside of any in the aquarium to begin with.


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## Diana Walstad (Aug 17, 2019)

Edward said:


> Can you expand on that please?


I picked 0.5 ppm CO2, a value frequently quoted by scientists, based on Wetzel's textbook*:

"The amount of CO2 dissolved in water from atmospheric concentrations is about 1.1 mg/l at 0 degrees C, 0.6 mg/l at 15 degrees C; and 0.4 mg/l at 30 degrees C." 

That's the concentration you'd expect to get if you set some distilled water exposed to the air overnight at room temperature (24 degrees C).

I measured the CO2 in my tanks. Early every morning, it was 3-10 ppm. (This is from overnight decomposition and respiration/breathing.) By afternoon, it went to zero as plants pulled it out of the water for their photosynthesis.

CO2 often limits plant growth. I discuss the shortage of CO2 in nature and in aquariums in the 'Carbon' chapter of my book _Ecology of the Planted Aquarium_.

*Wetzel RG. 1983. Limnology (Second Ed.). Saunders College Publishing (Philadelphia, PA), p. 202.


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## Edward (Apr 11, 2005)

Diana Walstad said:


> I picked 0.5 ppm CO2, a value frequently quoted by scientists, based on Wetzel's textbook*:
> 
> "The amount of CO2 dissolved in water from atmospheric concentrations is about 1.1 mg/l at 0 degrees C, 0.6 mg/l at 15 degrees C; and 0.4 mg/l at 30 degrees C."
> 
> ...


Thank you for posting this information. 
The experiment you are referring to was completed with distilled water. Atmospheric or compressed CO2 equilibrium with water is limited by the amount of carbonate. If there is not enough carbonate in the water then CO2 or H2CO3 will not complete its equilibrium. Since the above described experiment was done with distilled water it doesn’t reflect the concentrations achieved in aquariums where carbonates are usually higher the zero. 

_“When we substitute the carbon dioxide concentration, and solve for pH, we get

pH = 5.65

Since rain is in equilibrium with the atmosphere, this is the pH expected for natural rain. It is also the pH expected if the body of water is in equilibrium with the atmosphere, and does not contact limestone (e.g., CaCO3).”_

Reference:
Carbon Dioxide and Carbonic Acid


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## [email protected] (May 22, 2019)

Thank you guys for all your input. I see that the conversation got pretty heated though the point of my question was very basic.

Overnight the level of CO2 goes higher a little bit than the equibrium because of decomposing and respiration but when the lights come on the plants start to uptake so after few hours the level will drop to zero, as Diana mentioned. Question is, how can we maintain a stable 3-4ppm or what ever the equilibrium ppm is when the lights are on? So that when the plants uptake the CO2 we ca introduce atmospheric CO2 at a faster rate so that the plants don't ge to completely starv for CO2. 

Sent from my SM-G975U using Tapatalk


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## Amp2020 (Mar 8, 2013)

Place the aquarium at lowest level in your home and run a sump that sits on the floor. CO2 is heavier than air and will concentrate at the lowest areas of the home. In home CO2 levels can be much higher than out door atmospheric levels. Just ask anyone with a reef tank and a pH monitoring system. Having some friends over for a party can lower the tank's pH level due to increased CO2 from respiration of the people inside. Same thing can happen if using a fireplace or any kind of gas appliance. I could tell exactly when my wife turned on our gas oven just by the pH alarm notifications I would get from my Neptune controller. Also, my tanks with sumps always had higher CO2 levels than the tanks without sumps. You could probably get a similar effect by place a large air pump on the floor and kept a tight fitting glass lid to reduce the CO2 loss. It's true that the highest CO2 levels, during the day, you can achieve are the same as the ambient levels. But that certain areas in the home might have higher levels than outside. Some reef keepers will draw in air from outside and inject into their skimmers to help reduce the CO2 concentration levels.


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## Amp2020 (Mar 8, 2013)

You could also hook up a pH controller to the lights. When the pH gets too high, have the controller turn off the lights. Once the pH drops to a certain range, have the lights come back on. Diane Walstad was the first person I heard to describes this as a rest period. It allows the bio load in the tank to build up CO2 and then turn the lights back on. She suggested having the lights on for a few hours and then rest for a few hours. Then have the lights back on after the rest period. This has helped control algae in my low tech tanks. I still get some algae but not nearly as much.


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## Diana Walstad (Aug 17, 2019)

*Siesta Regimen*



Amp2020 said:


> Diana Walstad was the first person I heard to describes this as a rest period. It allows the bio load in the tank to build up CO2 and then turn the lights back on. She suggested having the lights on for a few hours and then rest for a few hours. Then have the lights back on after the rest period. This has helped control algae in my low tech tanks. I still get some algae but not nearly as much.


Right on! An afternoon "siesta" works well. I've measured a nice rebound in CO2 levels (e.g., from 3 ppm up to 8 ppm CO2) after a 4-hour midday Siesta (see Fig. XI-2 in my book, p. 179). I set timer to turn overhead lights off for a few hours around noon. 

Since plants are less adept than algae at getting CO2, the worst thing you can do is have intense light and scarce CO2. An afternoon siesta allows plants to compete better. In the afternoon, when you turn the lights back on, the plants have both CO2 and light.

Also, folks, keep in mind that the CO2 you measure doesn't tell the whole story. Say, I measure 4 ppm at 11 AM. Typical. It doesn't seem like much, but it could be enough for many plants. That's because the 4 ppm represents what's _leftover_ from what the plants have taken up. During the day, the plants are taking up CO2, but the bacteria/fish/plants are still generating CO2 via respiration and decomposition. I say this, because many people think that they have to maintain 20 ppm CO2 to grow plants effectively.


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## [email protected] (May 22, 2019)

@Amp2020, having a sump closer to the floor is a great observation. You say that Salt Water folks know well how this affects the water pH, which makes me wondering if CO2 dissolves better in salt water?

@Diana Walstad, the "afternoon siesta" makes a lot of sense, no one said that the 8 hours of light a day should be continuous light . Using a pH controller as @Amp2020 mentioned is a very cool automation but I suspect the controller should be pretty expensive. Also, my water dKH is 9 drops on API kit which is about 161 ppm so my pH is 7.6 rock solid and I don't think that even injected CO2 could shake it enough for the pH controller to detect it, especially in a tank that has not injected CO2 this fluctuations will be minimal. So, as a cheaper solution would be to just simply split the time period into two intervals with a couple hours break in between the intervals. This more or less should achieve the same results as with the controller since we definitely know that the plants will deplete the water of CO2 in a couple of hours. Unfortunately, my Beamswork timer doesn't allow me setting up a schedule like this but I will look forward into getting a more advanced timer.

This are some very good observations guys and exactly the kind of advice I was looking for! Keep it coming!


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## Streetwise (May 24, 2019)

The new Fluval firmware makes siestas really easy. I've been running with two siestas, plus ramp up and down for each photo period, and now I don't really have to worry about algae. 

PS, Diana, I love your book! I run three low-tech tanks with soil substrate, capped with sand and a little bit of gravel. They are so low-maintenance and relaxing.

I have an Apex Neptune system for monitoring and some control, and it is interesting to watch the pH and temp (even with no heater) move throughout the day.

Cheers,

Jason


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## Surf (Jun 13, 2017)

> pH = 5.65
> 
> Since rain is in equilibrium with the atmosphere, this is the pH expected for natural rain. It is also the pH expected if the body of water is in equilibrium with the atmosphere, and does not contact limestone (e.g., CaCO3).”
> 
> ...


OK, but we want to know the PPM in the water not the PH. According a table on this site:
Ocean acidification

A PH of 5.6 in pure water means the water has* 400ppm of CO2*. Which means the concentration in the air and in the rain drop just before it hits the ground are the same. However once the drop hits the ground it picks up minerals that can rChange the amount of CO2 in the water. 

I don't have pure water but I do use DO/DI water with a TDS of 1. Basically I put RO water in a bucket and use a small pump slowly pump it through a DI filter to get as clean as I can. I typically only check it with the TDS meter. So a couple of months ago I measured it with my. PH pen. So I measured it. and observed the following:

i1 it took my PH pen 6 hours to stabilize at a PH indicating a CO2 concentration of between 1000 and 200ppm.

I put and air stone in on liter to this water r and got the ph down to 5.8. in 24 hours.

I then took out the air stone to let it outgas. 4 days later the PH was unchanged. *it didn't outgas*. 

So basically water want to have about the same amount of CO2 in it as the atmosphere. And once it reaches equilibrium it stays there unless something ( like plants) removes it. 

Now I did know that using a PH pen on DI water can cause damage to the pen. But it was calibrated before the tests and after the test it appeared to be fine. But now 3 months later it died. 

Additionally experiements on farm fields have show that plants need a minimum of 170ppm of CO2 to survive. Most of the plants grown in aquariums are genetically very similar to none aquatic plants. So it is highly unlikely that CO2 levels inside of a CO2 injected aquarium are significantly less than 170ppm. 
https://biology.stackexchange.com/questions/29943/whats-the-or-some-of-the-minimums-amount-of-atmospheric-carbon-dioxide-need

Also drop checker don't measure the amount of CO2 in the tank water or the tank PH. Instead they detect the CO2 in the air bubble between the tan water and indicator pollution. So in my opinion the drop checker is measuring the amout of [email protected] outgassing from the aquarium. Based on my oberservations of the Ph of my DI water, water will only outgas CO2 if it has more CO2 than the air does. Which means the CO2 concentration in the water must be just above atmospheric levels for a drop checker to detect it.

So I think you can use a air pump to maintain adequate CO2 levels in an aquarium without resorting to CO2 injection. But I think it will take much more air flow than most aquarium pumps but out. Also you want very small bubbles chumming out of the air stone. Small bubbles take longer to reach the surface allowing more time for gas exchange to occur. That means you need a air stone like a CO2 diffuser. Most aquarium air pumps cannot produce enough air pressure to work with CO2 diffusers. 

But the biggest issue I see is how do we determine when there is enough air flow through the water. Chemicals CO2 test kits are sensitive to minerals in the water and may not work well. Same for PH probes and the drop checker. Getting the plants to pearl may be the only practical way to know.


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## Diana Walstad (Aug 17, 2019)

Surf said:


> OK, but we want to know the PPM in the water not the pH. [/url]
> 
> Chemicals CO2 test kits are sensitive to minerals in the water and may not work well. Same for PH probes and the drop checker. Getting the plants to pearl may be the only practical way to know.


I used a LaMotte test kit using the titration method and got the information I needed. It was easy to recognize predicted day time changes: early morning highs, the morning declines, and the big increases after the siestas. Tanks without siestas showed a steady decline all day and had 0 ppm CO2 by late afternoon, around 4 and 5 PM (my book, p. 179). 

During the measurements, I also monitored for pH changes (colorimetric method). I didn't see any, so the pH method was totally useless for my purposes. 

Changes in pH due to CO2 will be influenced *greatly* by the bicarbonate concentrations (KH) in the water. My water was very alkaline (well water with high KH during prolonged drought ) at year of measurements, so pH did not reflect CO2 changes very well. 

Measuring CO2 _directly_ is a good way of seeing what's really going on in a low-tech tank without having to resort to charts. (For high-Tech tanks, one combines both pH and KH information to determine CO2 indirectly via a chart.)


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## Deanna (Feb 15, 2017)

Diana Walstad said:


> I used a LaMotte test kit using the titration method and got the information I needed. It was easy to recognize predicted day time changes: early morning highs, the morning declines, and the big increases after the siestas. Tanks without siestas showed a steady decline all day and had 0 ppm CO2 by late afternoon, around 4 and 5 PM (my book, p. 179).
> 
> During the measurements, I also monitored for pH changes (colorimetric method). I didn't see any, so the pH method was totally useless for my purposes.
> 
> ...


I took a look at the LaMotte kit a few years ago, but decided against it, not because it was no good, but because it was no better than the nomographic method and, if one is confident in high precision of KH and pH measurements, the nomographic approach is better.

I based this upon LaMottes response to the question, if we can believe the poster. Discussions and LaMotte quotes can be found here:

https://www.plantedtank.net/forums/11-fertilizers-water-parameters/955-ph-kh-chart-vs-lamotte-co2-test.html#post6154

https://www.plantedtank.net/forums/11-fertilizers-water-parameters/17248-co2-readings-trust-lamotte-testkit-over-ph-kh-cross.html

LaMotte CO2 Test Kit - General Aquarium Plants Discussions - Aquatic Plant Central

Like virtually all tests, the typical interference in our tank water is problematic for the LaMotte as well and the LaMotte is dependent upon neutralizing (reading) the carbonic acid. Still, like others, the LaMotte kit is probably useful when comparing readings on a relative basis.


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## cl3537 (Jan 28, 2019)

Diana Walstad said:


> I used a LaMotte test kit using the titration method


Hello Diana so happy to have you participating here, love your work.

Just a question about the Lamotte Test CO2 Kit Carbon Dioxide Test Kit - 7297-DR-01 - Aquarium and Fish Farming - LaMotte

If its the one I linked, it is simply NaOH titration and phenolphthalein indicator and is just as useless(if not worse) for estimating CO2 as any simple pH measurements we reccomend here. Even a titration for the Carbonic Acid/Bicarbonate endpoint is useless. If the sample contains any acid, bases, or buffers other than the theoretical carbonate equilibrium the test is useless. Short of distilled/RO water all water from natural sources is bound to contain something that will invalidate that test.


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## cl3537 (Jan 28, 2019)

[email protected] said:


> @Diana Walstad, the "afternoon siesta" makes a lot of sense


I have read this from many hobbyists, however I have never seen a shred of conclusive proof that it was necessary or helpful. No properly conducted study that I know of has ever compared plant growth with or without a siesta nor demonstrated a significant difference against a control.


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## Deanna (Feb 15, 2017)

cl3537 said:


> I have read this from many hobbyists, however I have never seen a shred of conclusive proof that it was necessary or helpful. No properly conducted study that I know of has ever compared plant growth with or without a siesta nor demonstrated a significant difference against a control.


I can only offer anecdotal evidence for the siesta concept, but I do use it after having run repeated tests over many months, a few years ago. However, my objective is algae suppression as opposed to CO2 replenishment. 

The ‘theory’ postulated by many (searching will find it) as well as some biologists to whom I have access, state that algae is disrupted if light is withdrawn about every four hours, whereas plants are robust enough to handle it. I was able to convince myself (rightly or wrongly) that, in fact, there was some minor, but noticeable reduction.


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## Diana Walstad (Aug 17, 2019)

cl3537 said:


> Hello Diana so happy to have you participating here, love your work.
> 
> Just a question about the Lamotte Test CO2 Kit Carbon Dioxide Test Kit - 7297-DR-01 - Aquarium and Fish Farming - LaMotte
> 
> If its the one I linked, it is simply NaOH titration and phenolphthalein indicator and is just as useless(if not worse) for estimating CO2 as any simple pH measurements we reccomend here. Even a titration for the Carbonic Acid/Bicarbonate endpoint is useless. If the sample contains any acid, bases, or buffers other than the theoretical carbonate equilibrium the test is useless. Short of distilled/RO water all water from natural sources is bound to contain something that will invalidate that test.


Thank you. This forum is indeed a lively place!

The APHA (American Public Health Assoc.) describes the basic titrimetric test for CO2 that I used and that you have described. Its simplicity is a virtue. Reference: Greenberg AE, Clesceri LS, and Eaton AD (Eds). 1992. Standard Methods for the Examination of Water and Wastewater. (18th Edition). American Public Health Association (Washington, D.C.)

The APHA cautions not to use the titrimetric test on acid mine wastes, sea water or where the ferrous ion exceed 1 ppm--strange situations. The only other test the APHA listed for CO2 measurement is the chart method with KH and pH, which many high-tech folk use. Both are good. I believe that I was on solid ground using the APHA method, and it gave me the information I needed/wanted. The fact that I used a LaMotte test kit was incidental.


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## jeffkrol (Jun 5, 2013)

cl3537 said:


> Hello Diana so happy to have you participating here, love your work.
> 
> Just a question about the Lamotte Test CO2 Kit Carbon Dioxide Test Kit - 7297-DR-01 - Aquarium and Fish Farming - LaMotte
> 
> If its the one I linked, it is simply NaOH titration and phenolphthalein indicator and is just as useless(if not worse) for estimating CO2 as any simple pH measurements we reccomend here. Even a titration for the Carbonic Acid/Bicarbonate endpoint is useless. If the sample contains any acid, bases, or buffers other than the theoretical carbonate equilibrium the test is useless. Short of distilled/RO water all water from natural sources is bound to contain something that will invalidate that test.



Wouldn't consider it useless but there are issues..




https://www.sciencedirect.com/science/article/pii/002216949402628O


> Existing titration-based methods for the measurement of dissolved free CO2 are indirect and require the measurement of a number of other determinands (e.g. pH); they may underestimate free CO2 concentrations, because analysis is carried out frequently in an open vessel from which some free CO2 may be lost prior to measurement. Here, a method of headspace analysis is described; this minimises CO2 loss and provides a more direct technique for determining free CO2 in low ionic strength, organic-rich upland streamwaters.


https://reader.elsevier.com/reader/...7B585C120932EC92F9D0FBB79583B45502338E3412B5F


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## Diana Walstad (Aug 17, 2019)

[email protected] said:


> @Amp2020 Unfortunately, my Beamswork timer doesn't allow me setting up a schedule like this but I will look forward into getting a more advanced timer.


Any decent hardware store (e.g., Home Depot) should have cheap light timers (<$10) that you can program mechanically for hours on and off.


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## Diana Walstad (Aug 17, 2019)

jeffkrol said:


> Wouldn't consider it useless but there are issues..
> 
> https://www.sciencedirect.com/science/article/pii/002216949402628O
> 
> https://reader.elsevier.com/reader/...7B585C120932EC92F9D0FBB79583B45502338E3412B5F


CO2 outgassing into the air is always a concern and must be respected during direct CO2 measurements. Thus, when I did my measurements, I was mindful of CO2 outgassing. I measured CO2 within minutes of pulling water out of the tanks into the test tube, didn't shake the tubes unnecessarily, etc.

Ironically, this re-enforces a major point of mine. CO2 is easily lost by outgassing. It can be a major problem with air-stones, water turbulence, spillway filters, etc that facilitate air/water exchange.


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## jeffkrol (Jun 5, 2013)

Diana Walstad said:


> CO2 outgassing into the air is always a concern and must be respected during direct CO2 measurements. Thus, when I did my measurements, I was mindful of CO2 outgassing. I measured CO2 within minutes of pulling water out of the tanks into the test tube, didn't shake the tubes unnecessarily, etc.
> 
> Ironically, this re-enforces a major point of mine. CO2 is easily lost by outgassing. It can be a major problem with air-stones, water turbulence, spillway filters, etc that facilitate air/water exchange.



One doesn't need absolute precision to measure trends either..


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## Asteroid (Jul 26, 2018)

Diana Walstad said:


> ..I say this, because many people think that they have to maintain 20 ppm CO2 to grow plants effectively.


I'm not sure what your referring to here. In low-tech most realize they are not going to achieve 20ppm co2 so they use plants that work under those conditions. Most low-tech tanks generally operate under much less, but it's not going to work for all plants. 

Wouldn't the amount of co2 needed to effectively grow plants be directly related to light. In a hi-tech tank south of 20ppm many times isn't enough not only to grow certain plants effectively, but to grow them at a fast enough rate where the uptake keeps algae away.


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## cl3537 (Jan 28, 2019)

Diana Walstad said:


> Thank you. This forum is indeed a lively place!
> 
> The APHA (American Public Health Assoc.) describes the basic titrimetric test for CO2 that I used and that you have described. Its simplicity is a virtue. Reference: Greenberg AE, Clesceri LS, and Eaton AD (Eds). 1992. Standard Methods for the Examination of Water and Wastewater. (18th Edition). American Public Health Association (Washington, D.C.)
> 
> The APHA cautions not to use the titrimetric test on acid mine wastes, sea water or where the ferrous ion exceed 1 ppm--strange situations. The only other test the APHA listed for CO2 measurement is the chart method with KH and pH, which many high-tech folk use. Both are good. I believe that I was on solid ground using the APHA method, and it gave me the information I needed/wanted. The fact that I used a LaMotte test kit was incidental.


You may want to consider all the caveats published within those Standard Methods 4500-CO2, APHA, 1999. 

b. Interference: Cations and anions that quantitatively disturb the normal CO2-carbonate equilibrium interfere with the determination. Metal ions that precipitate in alkaline solution, such as aluminum, chromium, copper, and iron, contribute to high results. Ferrous ion should not exceed 1.0 mg/L. Positive errors also are caused by _*weak bases, such as ammonia or amines, and by salts of weak acids and strong bases, such as borate, nitrite, phosphate, silicate, and sulfide*_. Such substances should not exceed 5% of the CO2 concentration. The titrimetric method for CO2 is inapplicable to samples containing acid mine wastes and effluent from acid-regenerated cation exchangers. *Negative errors may be introduced by high total dissolved solids, such as those encountered in seawater, or by addition of excess indicator.* 

The nomographs and the equations on which they are based *are valid only when the salts of weak acids other than carbonic acid are absent or present in extremely small amounts.* Some treatment processes, such as superchlorination and coagulation, can affect significantly pH and total-alkalinity values of a poorly buffered water of low alkalinity and low total-dissolved-mineral content. In such instances the nomographs may not be applicable. 

For example my tap water is 8 - 8.2ph it is treated(I am uncertain of the exact processing) much like most municipal water supplies. It is predicted to be 7.7 by Carbonate theory (3.0ppm CO2 dissolved, kh=5, 25 Degrees C). This could lead to a ~50% error in the determination of my CO2 concentration, this has led me to the conclusion that both titration(lamotte) and using the Barr ph/kh/CO2 chart would not be accurate enough for my purposes.


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## MichaelLyle (Jul 17, 2012)

This


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## Oughtsix (Apr 8, 2011)

mboley said:


> I have heard conflicting info on whether I need to have a surface turbulance in my low tech/Excel tank.
> 
> Right now I have a single output from my cannister with quite a bit of flow. As water level decreases, I do get an air water mixture until I replenish with make up water. Do I need to avoid that at all costs? How much surface turbulence should I have? None?
> 
> If you could please clarify. Thanks


Where do your fish get oxygen to breath from without any surface agitation?... especially after lights out when your plants start absorbing oxygen and putting out CO2?

I run a sump with a trickle filter and no CO2 or excel dosing... my biggest complaint is that I have to prune my plants too often!


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## [email protected] (May 22, 2019)

Oughtsix said:


> Where do your fish get oxygen to breath from without any surface agitation?... especially after lights out when your plants start absorbing oxygen and putting out CO2?
> 
> 
> 
> I run a sump with a trickle filter and no CO2 or excel dosing... my biggest complaint is that I have to prune my plants too often!


Do you see your plants pearling when thr lights are on? Just curious. 

Sent from my SM-G975U using Tapatalk


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## Oughtsix (Apr 8, 2011)

[email protected] said:


> Do you see your plants pearling when thr lights are on? Just curious.
> 
> Sent from my SM-G975U using Tapatalk


Nope, usually no pearling since the tank balanced. Just excellent growth!


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