The dissolved gas / bubbles paradox

Nick72

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Let me preface this topic with my set up and PH Profile

50g (36x18x18) lightly planted
Fluval Planted 3.0
Fluval 407 canister
Ista PH Monitor

Aquarium water degassed = PH7

CO2 Schedule:
On 06:00. Off 13:00

Lighting Schedule:
Ramp up 09:30(PH6)-10:30 (PH5.8)
Ramp down 17:00(PH5.8)-18:30(PH5.9)

I would keep the CO2 on for longer but it just degasses to PH7 by 06:00 for the start of the CO2 schedule.

So the prevailing philosophy on this forum appears to be, and please correct me if I'm wrong, that the the target PH drop should be reached by lights on, and that it must remain completely stable for the full photo period.

So now for the bubble paradox.

I've read elsewhere that the distribution of CO2 bubbles, to the point where they make physical contact with each leaf is equally as important as the actual PH drop.

But as you can see from my PH Profile there are no undissolved CO2 gas bubbles in my aquarium for the majority of my photo period.

Further to this I've read countless posts on this forum expressing the importance of flow and circulation in regards to CO2.

Again a paradox to my PH Profile - clearly for the majority of my photo period I have reached my target PH through dissolved CO2 in the aquarium water.

A small body of water, in this case a 50g aquarium, with even a modicum of circulation, will evenly distributed any completely dissolved gas (in this case CO2), so why would circulation be an issue.

Do let me know what you think, because right now the two concepts appear contradictory, at least for my setup.
 

Zeus.

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Lighting Schedule:
Ramp up 09:30(PH6)-10:30 (PH5.8)
Ramp down 17:00(PH5.8)-18:30(PH5.9)

I would perfer it if the pH was 5.8 ish at lights on.

I've read elsewhere that the distribution of CO2 bubbles, to the point where they make physical contact with each leaf is equally as important as the actual PH drop.

Yes, if you have CO2 bubbles - I have reactors so have non.

What colour is your DC at say 12.30?

A small body of water, in this case a 50g aquarium, with even a modicum of circulation, will evenly distributed any completely dissolved gas (in this case CO2), so why would circulation be an issue.

Carbon dioxide in air has a diffusion coefficient of 16 mm2/s, and in water its diffusion coefficient is 0.0016 mm2/s

Assuming CO2 travels in a straight line
so in air takes CO2 22.5 secs to travel length of tank
in water takes CO2 225.000 secs (2.6 days) to travel length of tank
So in water plants need water movement and in high light tanks we need more water movement
 

JoshP12

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First, my disclaimer, "I have only recently grown plants without any deficiency, so take what I say with that in mind"

I've read elsewhere that the distribution of CO2 bubbles, to the point where they make physical contact with each leaf is equally as important as the actual PH drop.
But as you can see from my PH Profile there are no undissolved CO2 gas bubbles in my aquarium for the majority of my photo period.
Yep (I have no citation), Tom Barr showed something along the lines of, "there is a 25% increase in photosynthetic activity when you have co2 mist in a tank" -- he did this by measuring an increase in dissolved oxygen levels. It is just that there is a chance the mist will hit the plant and for that second in time there is no possibility that CO2 is a limited nutrient for - hopefully we get lots of photons hitting the leaf at that point.

In page 2 of this thread https://www.ukaps.org/forum/threads...sue-or-if-patience-is-the-virtue.60454/page-2 , I performed several approximations (with loads of error that I accounted for where I pick the number 1%) as I was battling this thought.

Further to this I've read countless posts on this forum expressing the importance of flow and circulation in regards to CO2.

A small body of water, in this case a 50g aquarium, with even a modicum of circulation, will evenly distributed any completely dissolved gas (in this case CO2), so why would circulation be an issue.

You are right - you really only need to ensure that at every point a photon hits the plant and begins the photosynthetic cycles that there is sufficient nutrients available. That would be why you couldn't grow plants as well in dead spots. That is also why carpets are harder. The only thing that low-velocity, high turnover flow does is increases the probability that these nutrients are available.

If you ramp up the light (you increase the number of photons that hit the leaf at each second) and you have "poor" flow, then you may start to see deficiencies by the reasoning above.

Cheers,
Josh
 

Nick72

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Thank you both for your replies.

That is interesting.

So the question I think I'm reaching is this.

For the majority of my photo period I am not providing my plants CO2 in the form of a mist.

Instead I'm providing a source of carbon in the form of carbonic acid.

Josh, you seem to be saying that Tom Barr would say that CO2 mist is at lest 25% better at providing carbon as a nutrient source than carbonic acid alone.

Is that correct. Or is carbonic acid even less effective than this?

In short do I need to change the what I'm doing?
 

JoshP12

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Josh, you seem to be saying that Tom Barr would say that CO2 mist is at lest 25% better at providing carbon as a nutrient source than carbonic acid alone.


I think it is more of a probability game - this is all based on memory - but those mist increase the chance of a collision, that increases the chance CO2 will be there during the time the photon hits. You definitely don't need the mist for good plant growth.

EDIT = deleted that other stuff - I misread the second quote. -- still calling @dw1305 -heh
 

dw1305

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Hi all
Josh, you seem to be saying that Tom Barr would say that CO2 mist is at lest 25% better at providing carbon as a nutrient source than carbonic acid alone. Is that correct. Or is carbonic acid even less effective than this?
I misread the second quote. -- still calling @dw1305
I don't know, but my guess would be that, when you have a mist of CO2 bubbles, some are getting trapped under the leaves etc and then that CO2 is passing straight into the plant via the stomata, or <"direct diffusion"> into the cells in Vallisneria etc.

I'm not a CO2 user, but you get this effect with air bubbles <"when you use a venturi"> on the filter outlet.

venturi2_zpsdxwhr1q8-jpg.jpg


cheers Darrel
 

zozo

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CO2 is passing straight into the plant via the stomata

I did read in several papers that aquatic plants or aquatic form of most bog plants are devoid of the stomata?. And the waterlily has its stomata at the upper side of the floating leaf. :) A few years back i did read a scientific report containing a listing of plant sp. and its morphology indicating having stomata or not. Unfortunately, i didn't bookmark it. At least not in the PC i'm currently working.

I have to do some digging to see if i can track it down again... :) Could even be, there was a thread here at UKAPS containing a link to this paper. It was to long ago to clearly remember. But i remember me finding it influenced by a UKAPS thread in this direction.
 

dw1305

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Hi all,
I did read in several papers that aquatic plants or aquatic form of most bog plants are devoid of the stomata?
They certainly have fewer stomata in the submerged leaves of (potentially) emergent plants. Obligate aquatic plants don't have stomata or a water resistant cuticle. If plants have fewer stomata, my guess would be that that is accompanied by a thinning of the cuticle allowing more direct diffusion, of gases, through the cuticle.
Could even be, there was a thread here at UKAPS containing a link to this paper.
<"Ranunculus repens in turloughs">?

cheers Darrel
 

zozo

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No it wasn't this one.. The one i'm referring to had a rather interesting large list, also tropical plant sp. with several morphology properties among other also listed Stomata Yes/No.

I usually always bookmark findings like this, but a few years back i had an HDD crashing beyond repair on my regular notebook and it is no longer accessible and i had no backup :(. I lost tons of bookmarks with it. I believe it was a study on aquatic and bog plant morphology (changes). It was a PDF written in Italic font. But what good is it to remember only that. Darn... :rolleyes: And there are quite a lot study articles out there on plants and their stomata. But stomata was not the key word in this one... Can't find it back.
 

dw1305

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