# Everything you want to know about CO2 and Aquatic Plants video



## mistergreen (Mar 3, 2007)

I'm planning to do a youtube video explaining CO2 & aquatic plants.
I don't have time now but might have some time soon. First I need to write a script for it. If any of the experts here want to contribute, please do.

I'll write the script and post it here. I'll start with an outline.

1. CO2
a. Atmospheric CO2 at 400, 407 ppmv. Explain parts per million by volume​b. CO2 in water: Explain partial pressure and ppm by weight or mass (mg/L)​c. Sources of CO2 in water, atmosphere & animals & decaying organics in the sediment (bacteria)​d. CO2 form carbonic acid in water, lowering the pH. Include CO2 speciation, CO2, H2CO3, CO3. Show speciation/pH concentration chart. Introduce the CO2,pH,kH chart, carbonate hardness, CO2 = 3 × KH × 10(7-pH). Remind that it only works in a pure water, with a little baking soda to control kH. A drop checker is a good, cheap approximation of CO2 concentration. If you need an accurate reading, it's best to have a CO2 sensor in the water or above the water using Henry's Law.​2. Plants
a. CO2 in water, a liquid, slower in diffusion, that's why plant need more CO2 and leaves physiology change to adapt to get more CO2. Compare that with terrestrial leaves.​b. CO2 function in plants​c. Usually aquatic plants can use HCO3, & CO3 too. Different enzymes are responsible for converting them to CO2.​


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## Maryland Guppy (Mar 5, 2015)

Daily consistency when using CO2.

Measuring pH drop. De-gassed vs. CO2 when lights on.

Two things that came to mind.


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## mistergreen (Mar 3, 2007)

Ah, co2 forming carbinc acid in water, lowering the pH is good point to mention.


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## Maryland Guppy (Mar 5, 2015)

Not just lowering pH but how many will target a 1.0 drop in pH whuch is approximately 30ppm of CO2.

The time delay when using a drop checker can be an issue.

Bubbles per second means very little, just confirmation of flow.

How to properly degass tank sample, air stone for 30 minutes.

Still thinking of more!


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## mistergreen (Mar 3, 2007)

Maryland Guppy said:


> Not just lowering pH but how many will target a 1.0 drop in pH whuch is approximately 30ppm of CO2.


I've done some reading on this. It all depends on the water chemistry, kH, pH... It works well in a controlled environment/ pure water environment like a drop check but isn't reliable in an lake/pond or planted aquarium.


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## hoppycalif (Apr 7, 2005)

mistergreen said:


> I've done some reading on this. It all depends on the water chemistry, kH, pH... It works well in a controlled environment/ pure water environment like a drop check but isn't reliable in an lake/pond or planted aquarium.


When the pH drops in aquarium water, as CO2 is added, the pH drop is an accurate measure of ppm of CO2, because no other parameter in the water has changed. If the water is allowed to outgas the CO2 until it is in equilibrium with the CO2 in the air, and if that leaves you with about 3 ppm of CO2 in the water, then the ppm of the tank water when it has CO2 added is 3 times 10 raised to the drop in pH power. So, if that drop is 1.0, there is about 30 ppm of CO2. If it is 1.2, there is about 50 ppm. (Note that this isn't accurate beyond about 1 significant figure, so it is 50, not 47.5 ppm.)


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## mistergreen (Mar 3, 2007)

hoppycalif said:


> When the pH drops in aquarium water, as CO2 is added, the pH drop is an accurate measure of ppm of CO2, because no other parameter in the water has changed. If the water is allowed to outgas the CO2 until it is in equilibrium with the CO2 in the air, and if that leaves you with about 3 ppm of CO2 in the water, then the ppm of the tank water when it has CO2 added is 3 times 10 raised to the drop in pH power. So, if that drop is 1.0, there is about 30 ppm of CO2. If it is 1.2, there is about 50 ppm. (Note that this isn't accurate beyond about 1 significant figure, so it is 50, not 47.5 ppm.)


Yeah, I wish it was that simple but chemists I've seen online are saying it's not that easy. The CO2 ppm depends on the water chemistry. It for sure works with pure water.


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## hoppycalif (Apr 7, 2005)

mistergreen said:


> Yeah, I wish it was that simple but chemists I've seen online are saying it's not that easy. The CO2 ppm depends on the water chemistry. It for sure works with pure water.


It isn't accurate to use KH and pH to measure ppm of CO2, because of the things in the water that affect pH and KH, other than CO2 and carbonates. But, when you use just one sample of water, and measure the pH with only the ppm of CO2 varying, it is as accurate as any of the other hobbyist methods for measuring CO2. The only part of this method which is questionable is the use of 3 ppm as the "no added CO2" ppm of CO2 contributed by atmospheric CO2. A 20% error in that 3 ppm number means a 20% error in the derived CO2. Chemists who don't think this method through are not qualified to make statements about the accuracy. (My opinion, of course.)


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## mistergreen (Mar 3, 2007)

I found this case for seawater & freshwater

http://www.soest.hawaii.edu/oceanography/courses/OCN623/Spring2012/CO2pH.pdf
Notice how CO2(aq) and other speciation concentration change depending on pH.


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## mistergreen (Mar 3, 2007)

I just read an post, luckily, usually aquatic plants can use HCO3, & CO3 too. Different enzymes are responsible for converting them to CO2.


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## mistergreen (Mar 3, 2007)

Did you guys know that there's a CO2 test kit, besides a drop checker?

http://help.bioworldusa.com/kb/algae-treatment/water-analysis-dissolved-carbon-dioxide-co2

Basically, you add a pH reagent (phenophthalein indicator) in x amount of water. Then you add per drop of sodium hydroxide solution (a base, not sure the concentration) until it turns pink. This will give you x amount of CO2 (mg/L) per drop.

https://www.hach.com/carbon-dioxide...N1f5v7sDJUZ6vBP-WVPnE-7Ipqd38T_BoC5u0QAvD_BwE


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## hoppycalif (Apr 7, 2005)

That link says: "Carbon Dioxide is present in water in the form of a dissolved gas. Surface waters normally contain less than 10 ppm free carbon dioxide, while some ground waters may easily exceed that concentration. Carbon dioxide is readily soluble in water. Over the ordinary temperature range (0-30 C) the solubility is about 200 times that of oxygen. Calcium and magnesium combine with carbon dioxide to form carbonates and bicarbonates.

Aquatic plant life depends upon carbon dioxide and bicarbonates in water for growth. Microscopic plant life suspended in the water, phytoplankton, as well as large rooted plants, utilize carbon dioxide in the photosynthesis of plant materials; starches, sugars, oils, proteins. The carbon in all these materials comes from the carbon dioxide in water.

When the oxygen concentration in waters containing organic matter is reduced, the carbon dioxide concentration rises. The rise in carbon dioxide makes it more difficult for fish to use the limited amount of oxygen present. To take on fresh oxygen, fish must first discharge the carbon dioxide in their blood streams and this is a much slower process when there are high concentration of carbon dioxide in the water itself."

I consider much of those three paragraphs to be nonsense, and some to be completely incorrect. If the test kit relies on that writeup being accurate, it isn't likely to be a good test kit.

Calcium and magnesium cannot exist in water, except as ions. The chemistry of those ions ending up as carbonates is not nearly as simple as that. Few plants get their carbon from carbonates. Lower dissolved oxygen in the water doesn't increase the CO2 concentration in the water. Fish, like humans, get rid of the CO2 in their blood routinely, and the concentrations of CO2 in the water that we see are not enough to interfere with the fish taking in O2.

If I am wrong, virtually all of the explanations of how CO2 acts in aquariums is wrong.


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## mistergreen (Mar 3, 2007)

I wouldn't take that link too seriously. I linked it for the instructions on using the hach co2 test kit.


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## mistergreen (Mar 3, 2007)

Just curious about the pH shift method for determining co2; would the pH buffer in a lake or aquarium affect the reading?


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## Maryland Guppy (Mar 5, 2015)

mistergreen said:


> Just curious about the pH shift method for determining co2; would the pH buffer in a lake or aquarium affect the reading?


Assuming that pH buffer is referring to alkalinity (dKH)

I have locally collected many plants always bringing home a water sample from the ponds or rivers.
Most often KH readings are near or at zero. Always less than 1dKH.
I also target <1dKH in my tanks but never zero.

If KH is truly zero very little CO2 will drop pH drastically.
This would make 30ppm of CO2 drop the pH into the 4's or possibly lower.
pH controllers are useless at this point, enough CO2 would not be delivered before the controller would cut off the solenoid.


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## mistergreen (Mar 3, 2007)

Maryland Guppy said:


> Assuming that pH buffer is referring to alkalinity (dKH)
> 
> I have locally collected many plants always bringing home a water sample from the ponds or rivers.
> Most often KH readings are near or at zero. Always less than 1dKH.
> ...


Yeah but what about people with kH (say 4-5dkH like me) in their tap water or lakes on a limestone bed?


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## Maryland Guppy (Mar 5, 2015)

mistergreen said:


> Yeah but what about people with kH (say 4-5dkH like me) in their tap water or lakes on a limestone bed?


pH controller would work in your tank with 4-5dKH just not when KH is zero.

There are options to lower KH too.
HCl can be used if RODI is out of the question.

Past year I have slowly been dropping KH in all my tanks.
Has made a big difference and improvement with @ least 75% species of plants.


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## mistergreen (Mar 3, 2007)

So the pH shift CO2 methods only work with <1dkH... It depends on the water chemistry then.

I thought it was weird this method is only used in this hobby and not in the scientific sector.


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## Maryland Guppy (Mar 5, 2015)

mistergreen said:


> So the pH shift CO2 methods only work with <1dkH... It depends on the water chemistry then.
> 
> I thought it was weird this method is only used in this hobby and not in the scientific sector.


No.
When there is no alkalinity/KH is zero pH will plummet/crash before you can add enough CO2 to get anywhere near 30ppm.

Many will now use a flow meter for zero KH applications.


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## hoppycalif (Apr 7, 2005)

Maryland Guppy said:


> Assuming that pH buffer is referring to alkalinity (dKH)
> 
> I have locally collected many plants always bringing home a water sample from the ponds or rivers.
> Most often KH readings are near or at zero. Always less than 1dKH.
> ...


There is a minimum pH that can be obtained with CO2 in the water. I don't recall exactly what that pH minimum is, but, as I recall, it is about 5.0 or a bit lower. It certainly isn't near 3.0. It has been 10 years and more since I read about this.



mistergreen said:


> So the pH shift CO2 methods only work with <1dkH... It depends on the water chemistry then.
> 
> I thought it was weird this method is only used in this hobby and not in the scientific sector.


In our hobby we use the change in pH method because we are dealing with typical planted tank water, with a KH around 3 or more (some plants need that much KH to do well, as I recall), with only the common fertilizer materials in the water in significant amounts, and with the two water samples taken close enough together in time that they can safely be assumed to be exactly the same, except for CO2. We also assume 3 ppm is a good number for degassed CO2 in the water. No scientist doing anything not related to hobbyist aquariums would use the method for measuring CO2. But, we don't have any really accurate ways to determine dissolved CO2, so it works fine for us. Also, remember, we don't have a good way to determine pH more accurate than +/-0.1, and considering that we are raising 10 to the power of that pH, that builds in considerable inaccuracy in our CO2 measurement. We are hobbyists!!


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## Maryland Guppy (Mar 5, 2015)

Carbonic acid could be as low as 3.68pH I believe.


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## hoppycalif (Apr 7, 2005)

I wish I could remember the article I read, a scientific paper, so I could see if my memory is still acceptable. I might have rounded off that pH in my mind to 4, or I might just have remembered wrong.


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## mistergreen (Mar 3, 2007)

I found another CO2 test kit, same as Hach but cheaper!
https://hannainst.com/hi3818-carbon-dioxide-test-kit.html

A tried and true method for CO2 is to look and the fish and plants. I think that'll be my #1 recommendation in the video and then test kits, then the pH shift, 3*10(pH1-pH2) & even the kH/pH 3*kH*10(7-pH) chart for specific water parameters.

There's nothing worse than overdosing fish. I've done it. Best to start out low. A planted tank can thrive with 15ppm like an NPT.


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## t2000kw (Jul 29, 2006)

You may already have considered this, but . . .

You first of all need to determine your target audience. It sounds like you're not aiming for the typical aquarium owner since you would quickly lose their interest in the technicality of all of it. 

If you're looking to reach the general group of aquarium owners, you'll need to cover simpler things first. 

How you do that is up to you, of course, but if you are aiming this for advanced plant aquarium owners who use artificial means to make the plants grow well, then you wouldn't need to bother with simplifying things or making it longer to first lay a foundation for the newbies out there. 

You have a choice of making this a CO2 for aquarium plants for dummies, or Advanced Methods for using CO2 in a planted aquarium.

I just thought that might help you work toward your goal, if you haven't already worked that out. Sometimes a writer (you, for the script) starts out not knowing exactly what to write until he or she can picture just what group of people they want to reach. 

Donald


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## mistergreen (Mar 3, 2007)

yup, I've been thinking about the audience this whole time. I was thinking making it light hearted but informational make it accessible for newbies and also something for medium to advanced audience to think about. I'll need a lot of animation.

I can't go into hard core science because that'll bore people and I'm not equipped.


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## t2000kw (Jul 29, 2006)

Sounds like you have a good handle on it. 

If you're a member of any related Yahoo or Groups.io groups, consider saving it also in PDF so you can upload it as a file for the group's use. 

Donald


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## mistergreen (Mar 3, 2007)

General question. I've heard people referring CO2 as steroids for plants. Can we call it food or just part of the list nutrients? Which I think is more apt.


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## hoppycalif (Apr 7, 2005)

CO2, or carbon, is one of the nutrients plants need before they can grow, and it is, I believe, the nutrient that is the most needed - plants contain more carbon than any other nutrient. It is needed so badly by plants that they change themselves to adapt to the availability of CO2. I would say it is the primary nutrient.


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## mistergreen (Mar 3, 2007)

yeah, protein & amino & carbohydrates are made up of carbon and all the nutrients Macro & micros are used to make them.


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