Effect of CO2 on Plant Growth at Low Light - The Planted Tank Forum
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post #1 of 162 (permalink) Old 09-07-2016, 04:18 AM Thread Starter
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Effect of CO2 on Plant Growth at Low Light

Years ago Ole Pedersen, et.al, wrote a scientific paper about Liebigs Law of minimums, related to light and CO2. Later the paper was simplified and was available on Tropica's website, as http://www.bio-web.dk/ole_pedersen/p..._2001_2_22.pdf In that article was a table of data showing the effect of light and CO2 on Riccia growth rates. That table was:


After studying that data for awhile I decided to plot it on a graph in a different way to see what I could learn. That gave me this:


This shows me that, for Riccia, it takes very little CO2 to get the full benefit of CO2 at light intensities up to at least 90 PAR, very high light. One reason for this is that Riccia is a low light, slow growing plant. It is reasonable to assume that other low light, slow growing plants would have given similar results.

Even high light plants, or fast growing plants probably give similar results, but with somewhat more CO2 needed to get the maximum growth rate. I grow Hygro corymbosa siamensis in my 30-35 PAR tank, and I see a similar result as that shown for Riccia.

I started growing the Hygro with no CO2, just Metricide as a carbon source. For over a month the Hygro struggled to grow, getting only a little bigger in a month. So, I added DIY CO2 at around 1 bubble per second. The Hygro immediately started growing much faster, so much so that I have been pruning about 4-6 inches off each plant every week.

To check how much I had affected the amount of CO2 in the water I put 0.5 dKH water in a drop checker and used it to monitor the CO2. With that low KH water, the range of measurement for CO2 is about 1 ppm to about 15 ppm. The first thing I noticed is that, with no CO2 on, the amount of dissolved CO2 rises back to around 3 ppm by the time I turn the lights back on, then drops down to around 1 ppm by the time the lights go off. That means the plants were using up the CO2 early in the photoperiod, something Diana Walstad also discovered in her research. (Her solution was a long rest period between lights on intervals, so the substrate could generate enough CO2 to restore the 3 ppm.)

With the CO2 on all day, the amount of dissolved CO2 goes to around 6-8 ppm. So, my improved growth of Hygro is caused by adding less than 10 ppm to the water. The other plants in the tank also are growing and looking much healthier with the CO2 on.

This was found to be the case years ago when DiY CO2 was first used. But, people continued to want more and more, so they increased their light intensity substantially, along with the CO2, and found that if they had 30 ppm the plants would grow much better at high light, and the fish would not be killed by the CO2. We then seemed to forget about the original benefits of CO2 on low light tanks.

I'm posting this to suggest that we stop telling folks that they need pressurized CO2 if they want to see any benefit in large tanks. It just isn't true. If we stick with low light, probably up to at least 40 PAR, we can gain big benefits for almost trivial additions of CO2, as long as we also dose Metricide or Excel, to stop the fluctuations in CO2 from triggering BBA attacks. This will greatly improve our success rate with our low tech tanks, and increase our enjoyment of the hobby.

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post #2 of 162 (permalink) Old 09-08-2016, 12:19 AM Thread Starter
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post #3 of 162 (permalink) Old 09-08-2016, 05:26 AM
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Forget adding CO2 and just blast the light. You'll get much faster growth. That's shown in the growth charts. Pedersen explained why in the paper. Applies to other plants as well. High light requires high CO2? Only if you still believe in grandpa myths. "Science progresses one funeral at a time." - Max Planck. Looking forward to some funerals so this hobby can advance.
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post #4 of 162 (permalink) Old 09-08-2016, 05:31 AM Thread Starter
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Originally Posted by Solcielo lawrencia View Post
Forget adding CO2 and just blast the light. You'll get much faster growth. That's shown in the growth charts. Pedersen explained why in the paper. Applies to other plants as well. High light requires high CO2? Only if you still believe in grandpa myths. "Science progresses one funeral at a time." - Max Planck. Looking forward to some funerals so this hobby can advance.
High light results in algae unless the plants are growing in good health. That requires that they have enough carbon available for the plants to do so. Even with low light the plants can strip the CO2 from the tank. I have to disagree with you.

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post #5 of 162 (permalink) Old 09-08-2016, 05:56 AM
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High light does not result in algae. That's another myth that needs to die. Excess nutrients, with light and CO2, results in algal growth. Algae are opputunistic organisms. They multiply when conditions favor their growth, which is a good thing since they remove excess nutrients. As long as there is a steady supply of nutrients, and as long as it doesn't become toxic, they grow.

Nutrients, light and CO2 are all required to culture algae. Limit CO2 and growth is proportionately limited. Same for the other two.
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post #6 of 162 (permalink) Old 09-08-2016, 07:38 AM
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If light energy drives demand(it does) for more CO2 and nutrient's than is available for plant's to draw from ,then algae which need's much less of everything ,will find excellent environment for proliferation.
Limit lighting, and increase CO2 availability, and provide basic nutrient's, and plant's will respond favorably with little if any algae.
Or you can choose to become a student of way's to combat various algae while blasting away with the light.
Your choice.

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Originally Posted by Solcielo lawrencia View Post
High light does not result in algae. That's another myth that needs to die. Excess nutrients, with light and CO2, results in algal growth. Algae are opputunistic organisms. They multiply when conditions favor their growth, which is a good thing since they remove excess nutrients. As long as there is a steady supply of nutrients, and as long as it doesn't become toxic, they grow.

Nutrients, light and CO2 are all required to culture algae. Limit CO2 and growth is proportionately limited. Same for the other two.
Yes algae multiply when condition's favor their growth.
Excess lighting,low/inconsistent CO2,and or possible nutrient limitation = poor plant health, which in turn trigger's many form's of algae.
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post #7 of 162 (permalink) Old 09-08-2016, 08:37 AM
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Quote:
I'm posting this to suggest that we stop telling folks that they need pressurized CO2 if they want to see any benefit in large tanks.
Well .. not quite true.. Pressurized CO2 can be run at trivial rates....like 1/2BPS..or less
To me pressurized CO2 is about convenience, regulation and repeat-ability. not to mention necessary for high pressure diffuses........Best to just mention that high CO2 concentrations may not be necessary..or even wanted..regardless of the light..
Now this really doesn't "quite" apply but I'm posting it just to show how things can become.. err.. unexpected..
Quote:
But results from the third year of the experiment revealed a more complex scenario. While treatments involving increased temperature, nitrogen deposition or precipitation -- alone or in combination -- promoted plant growth, the addition of elevated CO2 consistently dampened those increases.

"The three-factor combination of increased temperature, precipitation and nitrogen deposition produced the largest stimulation [an 84 percent increase], but adding CO2 reduced this to 40 percent," Shaw and her colleagues wrote.
Climate change surprise: High carbon dioxide levels can retard plant growth, study reveals : 12/02

"A man with a watch knows what time it is. A man with two watches is never sure"
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post #8 of 162 (permalink) Old 09-08-2016, 09:01 AM
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@Hoppy: good chart as it visually helps to understand the basic concepts.

The biggest point I got from it is how ROI is scewed: we go to much higher light and co2, at considerable labor and cost, to get that "extra" 1 -5 % in plant growth. It certainly upholds the old wisdom of the 80-20 rule.

I also find it telling how high ligh trails behind medium light curve until it catches up at that magic 30 ppm. I am guessing that the lag is attributable to the plants getting nutrients limited at higher light. All of this gives more support to Mr. Barrs' observations and decades-long assertions on light/co2/nutrients "arms race".

One area where our deductions might differ revolve around ricca as a test subject. My understanding is that ricca is closer to a marginal plant and actually derives more benefits from higher co2 then others. If that is indeed the case, then the benefits of much higher light and co2 would be even more questionable.

My personal experience with hygro corymbosa also differ a bit from yours: mine is currently under medium light, no injected co2, Excel twice a week at recommended dosage and all 5 of my plants grew 200-300% over the last couple of months. Given that, I would suspect that there is another variable between our conditions.

As in other discussions on the subject, yes - there are a lot of beatiful plants that do much better as emergent plants that we are trying to force 100% under water. They are the ones that we are trying to fool with high light and high co2. Luckily for us, there are a lot of more "reasonable" plants to chose from.

As to @Solcielo lawrencia, you might be right or you might be wrong but your message gets overwhelmed by the antagonistIc delivery style. I do want to hear your ideas and your rational for them if I could only filter them out from the noise.
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post #9 of 162 (permalink) Old 09-08-2016, 12:20 PM
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Quote:
Originally Posted by jeffkrol View Post
Well .. not quite true.. Pressurized CO2 can be run at trivial rates....like 1/2BPS..or less
To me pressurized CO2 is about convenience, regulation and repeat-ability. not to mention necessary for high pressure diffuses........Best to just mention that high CO2 concentrations may not be necessary..or even wanted..regardless of the light..
Now this really doesn't "quite" apply but I'm posting it just to show how things can become.. err.. unexpected..

Climate change surprise: High carbon dioxide levels can retard plant growth, study reveals : 12/02
Rubisco mechanisim in aquatic plant's is said, according to paper's on the topic, to take maybe week's to adapt to fluctuating CO2 level's or sudden shift's high to low CO2 level's, or vice versa.
Perhaps this contributed to observation that increase in CO2 brought no more improved growth over how long??
Or there was simply no more growth because the plant(s) studied had reached their potential height?
If Rubisco mechanisim is working hard to produce enzymes and suddenly more CO2 is available,then the enzyme production is not needed as urgently, and rubsico mechanisim adapt's accordingly and some lag time with growth could be expected?
Same lag time with sudden decrease in CO2 availability while enzyme production might need ramped up?
Surely some speculation on my part , but is a hint of supporting evidence which is more than some provide.
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post #10 of 162 (permalink) Old 09-08-2016, 12:42 PM
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very nice
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post #11 of 162 (permalink) Old 09-08-2016, 01:16 PM
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What is the point of continuing to use Excel? Excel is a algaecide rather than a carbon source. I think this is the root of the myth that CO2 prevents algae versus people recognizing the situation for what it is. Yes, a carbon source will help speed the growth of plants which in return will deplete nutrients so algae is kept at bay, but that doesn't happen overnight.

What is even more interesting about these types of experiments is that there is never any mention of how CO2 is being grabbed from the atmosphere. I'm not convinced that if a tank is in a room that never gets aired out via a open window does not see a increase of CO2 levels. Of course depending on where a person lives plays a key role as the air out in the middle of nowhere in Nebraska is going to be much different than downtown NYC.

The tanks we keep are not closed, sealed systems. Water grabs all kinds of things so I'm not sure why people would think CO2 is only limited to what comes out of a plastic bottle or canister.
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post #12 of 162 (permalink) Old 09-08-2016, 02:34 PM
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Quote:
Originally Posted by Solcielo lawrencia View Post
High light does not result in algae. That's another myth that needs to die. Excess nutrients, with light and CO2, results in algal growth. Algae are opputunistic organisms. They multiply when conditions favor their growth, which is a good thing since they remove excess nutrients. As long as there is a steady supply of nutrients, and as long as it doesn't become toxic, they grow.

Nutrients, light and CO2 are all required to culture algae. Limit CO2 and growth is proportionately limited. Same for the other two.
While this is true, it can be difficult to provide high light and avoid the types of conditions that would promote algae growth. If you blast light in a tank that is not up to the challenge (and IMO most people's tanks' aren't) then algae should blow up.

I do agree that even small amounts of CO2 around 10ppm can improve growth quite a bit without really risking algae outbreaks. Solcielo is right in saying that higher light will give you much faster gains - but IMO it is much riskier in terms of algae.

Basically you can't go wrong by injecting 10-30ppm of CO2 in any tank. You CAN go wrong by hitting your tank with a lot of light.


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post #13 of 162 (permalink) Old 09-08-2016, 04:58 PM Thread Starter
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Originally Posted by OVT View Post
@Hoppy: good chart as it visually helps to understand the basic concepts.

The biggest point I got from it is how ROI is scewed: we go to much higher light and co2, at considerable labor and cost, to get that "extra" 1 -5 % in plant growth. It certainly upholds the old wisdom of the 80-20 rule.

I also find it telling how high light trails behind medium light curve until it catches up at that magic 30 ppm. I am guessing that the lag is attributable to the plants getting nutrients limited at higher light. All of this gives more support to Mr. Barrs' observations and decades-long assertions on light/co2/nutrients "arms race".
Look more carefully at the chart. The growth rate on that chart is shown as the percent of the maximum growth rate at that light level. It shows how much CO2 it takes to get the maximum growth rate the light level permits. With very high light, that maximum growth rate is very high, and it takes a lot of CO2 to reach it. With low to normal high light, that growth rate isn't nearly as high, so it takes a lot less CO2 to reach it.

My interest is in low to medium light tanks, solely because I don't enjoy battling algae problems, and the lower the light level the fewer algae problems pop up. This chart clearly suggests that we can use almost trivial additions of CO2 and still get almost as good a growth rate as we would get if we followed the myth that 30 ppm is what is needed for CO2 to be effective for all light levels. I don't dispute that many plants need high light and high CO2 to reach their potential growth rates and beauty.
Quote:

One area where our deductions might differ revolve around ricca as a test subject. My understanding is that ricca is closer to a marginal plant and actually derives more benefits from higher co2 then others. If that is indeed the case, then the benefits of much higher light and co2 would be even more questionable.

My personal experience with hygro corymbosa also differ a bit from yours: mine is currently under medium light, no injected co2, Excel twice a week at recommended dosage and all 5 of my plants grew 200-300% over the last couple of months. Given that, I would suspect that there is another variable between our conditions.
I'm not sure our H. corymbosa experience is much different. I like having to prune the plant every week or two. Over a couple of months my H. corymbosa also roughly doubled in size, but other plants in my tank just didn't look healthy. Clearly, other species would react to CO2/light somewhat differently than Riccia did, but I believe my experience with H. corymbosa shows that the difference, for that plant, and thus likely for many low light plants, isn't much different.
Quote:

As in other discussions on the subject, yes - there are a lot of beautiful plants that do much better as emergent plants that we are trying to force 100% under water. They are the ones that we are trying to fool with high light and high co2. Luckily for us, there are a lot of more "reasonable" plants to chose from.

As to @Solcielo lawrencia, you might be right or you might be wrong but your message gets overwhelmed by the antagonistIc delivery style. I do want to hear your ideas and your rational for them if I could only filter them out from the noise.

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post #14 of 162 (permalink) Old 09-08-2016, 05:36 PM
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What is the point of continuing to use Excel? Excel is a algaecide rather than a carbon source. I think this is the root of the myth that CO2 prevents algae versus people recognizing the situation for what it is. Yes, a carbon source will help speed the growth of plants which in return will deplete nutrients so algae is kept at bay, but that doesn't happen overnight...
One more conspiracy by a large corporation lying to the ignorant consumer in order just to make a profit?
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post #15 of 162 (permalink) Old 09-08-2016, 07:23 PM
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Yes algae multiply when condition's favor their growth.
Excess lighting,low/inconsistent CO2,and or possible nutrient limitation = poor plant health, which in turn trigger's many form's of algae.
This is the same plagiarized explanation that's been repeated ad nauseum. There's no evidence to support such a belief. Quite the opposite. Plants grow in the presence of low co2, low nutrients, and can do so without I'll effects even under high lighting. Pedersen shows this as anyone else who grows healthy plants without adding either.

Plants grow slower when limited in resources but that alone doesn't cause algae. If nutrients are limited, so too are algae. There can be both healthy plants and healthy algae simultaneously. The presence of algae does not mean plants are in I'll health, which is another myth that needs to die.

Repeating myths does not make it quantifiable true. It only slows the pace of progress, which has been sorely needed for quite some time.

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I don't dispute that many plants need high light and high CO2 to reach their potential growth rates and beauty.
When you see for yourself what supposedly "difficult " plants look like when grown under no added CO2 (except for organismal respiration) but tremendously high, 150+ PAR lighting and no algae growth, would you accept that adding CO2 just isn't necessary under such conditions? Because once you have examples that show the dogma isn't true, then the dogma is falsified.

Last edited by Solcielo lawrencia; 09-08-2016 at 07:33 PM. Reason: Dp
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