Fluctuating CO2 Levels

jaypeecee

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Hi Folks,

Would anyone care to quantify fluctuating CO2 levels? This term crops up a lot but exactly what does it mean? The word 'fluctuating' refers to something that varies with time. So, when we refer to fluctuating CO2, are we referring to CO2 levels that vary throughout the photoperiod after stabilization? By which, I mean once the CO2 level has built up and settled to some level before the lights come on? Or, are we talking about variations in CO2 concentration from day to day? And how much fluctuation is considered acceptable? If we use a drop checker, it is so slow to respond that many fluctuations are undetectable.

JPC
 

Zeus.

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Fluctuating CO2 refers to the [CO2] changing thoughpout the 'Main' photoperiod and also from day to day.

D Wong sums it up well here IMO

the reasons why we dont wont it fluctuating are
we know that when the plant senses that high concentrations of CO2 is available, it responds by reducing the production of expensive Rubisco. When it senses a lower CO2 concentration it must increase Rubisco production, however because this protein is so complicated and heavy, the increased production requires 2-3 weeks in order to change the density in the leaf to match the new gas concentration level. So it is much easier to reduce production than it is to increase production. When increasing gas injection therefore, it hardly takes any time to see an improvement in health. When lowering the concentration, the plant will suffer because it must now ramp up Rubisco production to account for the loss of CO2 availability.

When increasing the light, the plant must reallocate resources from Rubisco production/maintenance in order to deal with the increased radiation. This may entail new pigment production for protection. When the light is reduced, the plant then reallocates the light gathering proteins and can devote them to Rubisco production/maintenance.
also worth note is

What I mean is that if you are struggling with CO2 stability, or are having difficulty keeping high concentrations, then it's best to focus efforts on the first half of the photoperiod and not worry so much about the second half. If you are running very strong lighting then you are really pushing the plants and it's necessary to have the CO2 going. After 4 hours, if you turn the gas off, the water stays saturated for a couple of hours after the valve closes and the concentration trails off. So if you have an 8 hour photoperiod and you turn the gas on 2 hours before lights on, you can turn the gas off after 6 hours. So the gas is still running for 8 hours but it's on-off cycle is offset by the amount of time you turn it on prior to lights on.

There is no need to run the gas for 10 hours therefore.

Plants don't really run their photosynthetic machinery for the full day anyway. Under normal conditions, after 4 hours or so they start to shut down, so that's why CO2 isn't really needed for the full photoperiod.

Long photoperiods benefit algae more than they do plants, especially if it is high intensity.
The long photoperiod is more or less for our enjoyment.
So consentrate from lights on and the first 4-5hours of the photoperiod ;)

And how much fluctuation is considered acceptable?
well it all depends what works IMO/IME - in a perfect world

upload_2019-10-10_21-48-35.png


I think I have got close to the perfect solution in stable [CO2] but it cost quite a bit and uses a PLC and duel CO2 injection and CO2 reactors and some software design to have the two injectors on the pH drop time and one on only once the pH is reached and then a little on and off as the light intensity increases and on fully when the intesity is maxed out. It may be a little OTT OFC but works for me.

But IMO a pH which is stable to within 0.1pH for the main photoperiod is very acceptable and that what mine is, but then the measurement of the pH is dependant on what is also used to measure the pH :arghh:

Can take a lot of trail and error to get it right and take weeks to months to get it right, change one thing eg CO2 injector or light and start again with the pH profile.

Also remember FLOW is KING and if the flow is inadequate the [CO2] will be fluctuating all over the tank locally at the leaf, as the flow is needed to keep the [CO2] stable at the uptake points on the leaves as the plant sucks up the CO2
 

alto

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Intuitively I’ve always been sceptical, it doesn’t make evolutionary (biochemical) sense for plants to be that rigid ...
and there are recent (I consider this to be the last 5 years or so ;)) papers studying various CO2 mechanisms in plants

Stable CO2 is fine :)
But erratic CO2 is not the end of anything

CO2 is much easier to manage in soft, acidic water re plants grow “better” in soft water, algae is less of a problem in soft water etc type statements (though there may also be (ie there is likely) biochemistry pathways that contribute


(Disclaimer: unlike Karl I never check my pH or CO2, as long as the plants look good, the fish and shrimp appear happy, algae is minimal ... that’s good enough
and ohhhhh, I’ve never had more than 6x turnover in any of my tanks, 2-4 times was more realistic estimate
Look at Filipe Oliveira’s 80cm home tank running on a moderately size AquaClear (I think that’s the brand) HOB - and whatever tap water and lean water column nutrients :) )
 
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jaypeecee

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Hi Zeus and alto,

Thanks for the feedback.

One way to control CO2 fluctuation is to use a CO2 controller such as those from JBL, etc. But, I believe they use a pH probe in the tank water itself. If so, that will be affected by acids other than carbonic and non-carbonate buffers in the water. And I don't understand how they manage to prevent build-up of bio film, algae, etc. on the probe itself - all of which must surely affect the accuracy of the pH reading.

I'll leave it at that for the moment but I will post again soon - possibly tomorrow.

JPC
 

Zeus.

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CO2 is much easier to manage in soft, acidic water re plants grow “better” in soft water, algae is less of a problem in soft water etc type statements (though there may also be (ie there is likely) biochemistry pathways that contribute
From my reading forums, PMs, talking to scapers and scaping shops and observations from visits to LFS, Aquaimium Gardens, Green Aqua and Takashi Amano Forests Underwatter at Oceanarium Lisbon. Soft water does seem to make plant growing easier as it avoids the complex interactions with hardwater in the way the ferts interact with the minerals in the water and to the life of the aqua soil itself.

Even my LFS uses RO/tap water mix in its show tank.

So much much depends on your tap water OFC and the harder your water it harder it seems to control CO2 and Ferts
 

Zeus.

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CO2 fluctuation is to use a CO2 controller
Have one and the prode drifts in is measurement so needs regular calibration and the pH swings at least 0.1pH between CO2 on and off. Plus its doesn't allow for the changes in the baseline pH of the tank water over the week. Only use it for a quick pH check use my PLC alone these days to control on off times of the CO2
 

papa_c

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Really interesting discussion...I live 2 miles from AG and the water here is very hard....they use water straight out of the tap as I do....I can not get my plant growth anywhere near theirs....my belief is maintenance is the key....ensure everything is scrupulously clean...I'm embarking on a severe cleaning regime to see if this improves the plant growth and algea control.
 

Siege

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Hi @papa_c

Yes maintenance makes a massive difference in the look of the tank and it being algae free. It certainly helps the plants but I do not think it is the be and end all in plant growth.

A couple of thoughts/findings -

Strong soft flow assists co2 and as such go hand in hand. Hardscape and plant mass have a part to play in this.

Light secondary but incredibly important. From what we have found ‘light is light’ is not true and spectrum along with good diffusion should be the goal.

Our biggest head ache over the past month has been a temporary display with spray bar and just white light above.
We have found these 2 factors have made the maintenance regime much more intensive and plant growth has been suffering from the direct flow, almost pointy jet of the spray bar. It requires much more fine tuning.

Maybe combined with lack of oxygen, again caused by the spray bar. We are unsure how much, but this is definitely a factor.

Nb. We do not test the ph instead rely on the CO2 coming on early to gain the early part of the photo period.
 

Siege

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Ps. Apologies for going slightly off subject with the above. I believe that co2, flow and light (along with oxygen perhaps) should be seen as one. Getting the balance ‘right’ is the hard bit and perhaps the holy grail! :)
 

jaypeecee

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From what we have found ‘light is light’ is not true and spectrum along with good diffusion should be the goal.
Hi Siege,

Yes, I strongly agree with your comment about light spectrum. But I am very much aware that others think otherwise. The photosynthetic absorption spectrum clearly shows that not all light wavelengths create the same response in plants. See the attached image. I am also aware that absorption of light is not the whole story. It's further complicated by how the plant uses specific wavelengths of light. If necessary, we could start a new thread on this subject - unless one already exists.

JPC
 

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Tim Harrison

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jaypeecee

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Spectrum, or the quality of light, is something I've thought of as important for sometime...Spectrum doesn't matter...does it?
And take a look at this early-ish research...Effects of Light Quality on Growth and Chlorophyll Composition in Hydrilla (T.K. Van et al)
Hi Tim,

Many thanks for pointing me to the above links, both of which I have now read. When I see references to red, green, blue or indeed any other colour light, we need to be specific about wavelengths (in nanometres). This is particularly true for LEDs, which often emit light within a very narrow band. Some red LEDs, for example, do not emit any significant light that correlate with the 642nm and 662nm peaks of chlorophyll b and chlorophyll a, respectively. But that's just the beginning...

JPC
 

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