CO2 in situ meter measurements, real time data on localized CO2 ppm readings

VaughnH

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If the volatility or transient nature of CO2 were a big contributor to the variations around the tank, there would be a major gradient from top to bottom, because the loss of CO2 would occur at the surface, depleting that layer, leading to the gradient. If the variations in CO2 in the water are due to plant usage of it, then the usage of all of the nutrients would cause similar variations in all nutrients throughout the tank. Doesn't that have to be true? Is another factor the changing state of the CO2 - from disolved CO2 to carbonic acid to carbonates and back and forth? I have no idea how dynamic that transformation is.
 

ccLansman

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this discussion makes me wonder if i need to pull out the periodic table and figure out atomic masses. Wouldent certain ions fall to the bottom of the tank as they are heavier then the solution they are in? So for instance how can there be a gradient of nutrients if some sink and some swim? :)
 

VaughnH

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The nutrients in our tanks is in the form of ions, which are dissolved in the water. I think the only time their atomic weight could affect the distribution would be if you were to centrifuge the water, to greatly increase the "gravitational" force on the solution. That would slightly increase the concentration at the farthest point from the rotational axis. That's how gas centrifuges work to enrich uranium. (All ions take YMCA swim classes at an early age, thus can swim very well.)
 

Tom Barr

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VaughnH;27812 said:
If the volatility or transient nature of CO2 were a big contributor to the variations around the tank, there would be a major gradient from top to bottom, because the loss of CO2 would occur at the surface, depleting that layer, leading to the gradient.

I wonder though, it seemed that the flow and exchange in the plant beds was lower based on CO2 meter readings.

CO2 is much larger an issue than say NO3, which plants can store and hold large reserves in their vacuoles, carbon as well, but not as CO2. I mean that in a short time frame, the CO2 can change by a very large amount. Seems the CO2 gradient is current and plant driven here.

Plants reduce the current and thereby exchange of CO2.
The demand for NO3 is much less, but it may still certainly occur and does in some systems according some research.

More current(up to the point, not more than say 2 mph) is good and reduces the boundary layer, so that not only CO2, but also NO3, PO4 etc get to the plant easily.

The CO2 mist and micro bubbles might break this boundary layer up and add more CO2 to localized regions(you can see the gas going into the plant beds).

This confirms the CO2 mist theories I've had as well...............

Some claimed it was homogeneous throughout the tank.
Yet once again these same folks and critics did not bother to test or devise a test to see if their claim or my own was valid or not. I'll let the evidence and the test stand for themselves.

In the meantime, crow shall be served to the critics.
Perhaps the calibrated meter and the settling time at each data point was all wrong?

I doubt it.
Done this and taken plenty of gas readings for O2 as well to get fooled here.

So perhaps my tanks (all 5 of them and a client's tank) are different due solely to chance? 6 replications seems pretty unlikely for that to occur.

Maybe the high light tanks and the venturi mist played some role, I do not doubt this, but if you are going to see a variation, adding high current and an very efficient and responsive CO2 delivery method seems wise to get the most effective result.

At high flows, we would expect to see less differences between the water column in the open vs the plant beds. Or with poor responsiveness from the CO2 delivery system. Or at low light intensity and low nutrient levels.

So you can see how to slant the set up design to favor and rule out other possible interactions? Much like using EI to rule out nutrients as a limiting factor. What other things might cause poor CO2 uptake in plants?
Then go about ruling everything else out, step by step.

If the variations in CO2 in the water are due to plant usage of it, then the usage of all of the nutrients would cause similar variations in all nutrients throughout the tank. Doesn't that have to be true? Is another factor the changing state of the CO2 - from disolved CO2 to carbonic acid to carbonates and back and forth? I have no idea how dynamic that transformation is.

Perhaps, but the plants cannot store that much CO2 say relative to N, P, K.
This is even more true in limiting or leaner system, so what might this mean then? .........something to ponder...........
I do not think the state of H2CO3[aq] CO2[aq] is really an issue, it'll equilibrate pretty fast in our system.
Why? Because about 400 CO2's for each H2CO3 is present for the ratio of Carbonic acid to CO2, this why CO2 is a weak acid, most is in the form of CO2.
Our blood seems to have no troubles at high rates, nor fish blood, we are adding a lot of CO2 as well to keep it "stable" also.

Regards,
tom Barr






Regards,
Tom Barr
 

ccLansman

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I have to agree with you Tom on the co2 misting idea, when the co2 is not misting at all seems to take a heck of a lot more BPS to get the plants pearling, but when a nice even mist is comming out of the spray bar the plants start pearling faster, more, and takes less BPS to due so.

Also Tom, just read your notes on co2 misting and exposing plants to air and then back into water. Did you ever gather any findings from this?
 

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ccLansman;27824 said:
I have to agree with you Tom on the co2 misting idea, when the co2 is not misting at all seems to take a heck of a lot more BPS to get the plants pearling, but when a nice even mist is coming out of the spray bar the plants start pearling faster, more, and takes less BPS to due so.

Also Tom, just read your notes on co2 misting and exposing plants to air and then back into water. Did you ever gather any findings from this?


Well, the CO2 mist also shows up as high dissolved levels as well.

Not just the gas phase.

I'm not sure how the air exposure really affected, it's nice if you can do it, makes the plants grow well and beats up on algae good.
But it often takes massive water change, so......there's a trade off there.
I do not like to do more than say 70% for the fish.

The real point about all this is really how well CO2 is dissolved without interferences in it's measure and in real time. That it is variable, and current is more than likely the main factor, and this is due to the denser plant beds.

This seems like a safe conclusion.

So at the end of the day: more current directed into the plants with CO2 mist seems like the best solution for effective growth, fish appear to be more tolerant of CO2 than previously thought, but it really depends on how and where you measure the CO2.

Regards,
Tom Barr
 

Tom Barr

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Here's some research references on flow in plant beds:

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http://www.cosis.net/abstracts/EGU2008/04017/EGU2008-A-04017.pdf?PHPSESSID=

this paper is of particular interest:

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11x lower flow/turbulence inside the plant beds and how differences in plant species can influence things.

I've blocked parts of my tank to reduce water flow, this had dramatic impacts on many plant species(poorer growth, algae etc).

Wiley InterScience :: Session Cookies

Basics:

Aquatic Weed Management in Citrus Canals and Ditches

Also, there's a BR newsletter that deals with current.



Regards,
Tom Barr
 

Carissa

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Applying this to diy co2 users....the previous thinking seemed to be that circulation should be somewhat reduced, in order to prevent excessive off-gassing of co2. But according to this, perhaps maintaining something closer to 10ppm of co2, with extremely good circulation, would be more advantageous to diy users than having a nice greenish yellow drop checker, by restricting circulation to get there.
 

ceg4048

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Tom Barr;27826 said:
Here's some research references on flow in plant beds:

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Tom,
I'm not sure if I'm just being thick skulled here but from what I'm able to see from the abstract in this first link their data appears to suggest the opposite:

...Studies of aquatic macrophyte communities at three sites on the Bow River, Alberta, Canada, between 1982 and 1985 showed that biomass decreased with increasing current velocity within the weed bed over the range 0.01-1 m/s [0.022-2.23 mph]; at current speeds in excess of 1 m/s [2.23 mph], aquatic macrophytes were rare....These results indicate that current velocity is an important factor regulating aquatic macrophyte biomass in flowing waters and suggest that even a relatively modest increase in current velocity within weed beds reduces the abundance of submerged aquatic plants...

They appear to blame the biomass reduction as a function of a rather vague "...direct effects of current velocity on plant shoots and its indirect effects on sediment nutrient concentrations..." whatever that means.:confused:

No discussion is made of CO2 (at least in the extract that I could view).

The introduction page further states:

...ecological studies have failed to show any consistent relationship between water movement and the distribution and abundance of submerged plant communities. For example, in the River Lambourn, Southern England the 1971-1980 expansion and recession of Ranunculus beds was positively correlated with discharge rate, whereas in the River Wye, Wales, macrophyte cover and peak biomass were negatively correlated with flow. Similarly, in a Swedish stream, Nilsson (1987) observed that macrophyte cover increased at low current velocities (
 

Tom Barr

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Carissa;27828 said:
Applying this to diy co2 users....the previous thinking seemed to be that circulation should be somewhat reduced, in order to prevent excessive off-gassing of co2. But according to this, perhaps maintaining something closer to 10ppm of co2, with extremely good circulation, would be more advantageous to diy users than having a nice greenish yellow drop checker, by restricting circulation to get there.

Well, they have trouble adding enough CO2 to begin with, that's most of the issue.
If they simply add another bottle, much like giving the needle valve another twist, then it's not an issue.

The other issue there is how they add CO2, with the internal reactor I designed and has been copied in general for the last few years, the results are very good. I cannot say for the other designs.
I had little trouble however with DIY.


Regards,
Tom Barr
 

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ceg4048;27831 said:
Tom,
I'm not sure if I'm just being thick skulled here but from what I'm able to see from the abstract in this first link their data appears to suggest the opposite:



They appear to blame the biomass reduction as a function of a rather vague "...direct effects of current velocity on plant shoots and its indirect effects on sediment nutrient concentrations..." whatever that means.:confused:

No discussion is made of CO2 (at least in the extract that I could view).

The introduction page further states:



Again, the CO2 variable was not addressed. Is it possible that the inverse relationship observed in these studies between current flow and macrophyte biomass would have been due to simply lower dissolved CO2 concentrations at those individual locations?

Cheers,

Look at the velocities.
As you get up to above 1-2 mph, then the weeds are ripped out.
So biomass will go down, this is mechanical shear, there's a trade off as we know between good current and uprooting plants all over.

Typically, in natural water ways, no flood control etc, the weeds are blasted out each year, if not, then the weeds clogged canals, rivers etc.

This is more what they where looking at.
At high areas/regions of flow, would expect sedimentation to occur? Accumulation of detritus?

Nope.

In areas of low flow, eg, inside the weed beds, would you expect to see more sedimentation and thus more dertrial accumulation and thus more richer composted soils?

I would.

So the data and conclusion makes pretty good sense.

I'm not suggesting to add more than 1mph of flow in our tanks:)
This gave the upper limits.
A general graph would show a bell shaped curve for plant biomass(Y axis) and flow velocities(x axis).

This same general bell shape is also true for species diversity(intermediate disstubance hypothesis, (Joe O connell)) and most organisms in flowing water.


As far as CO2 in real plant beds, this is virtually never measured.
Seems weird to me that they have not, perhaps the water samples vs real time data and the availability of a 2000$ probe.meter etc caused this.

They mostly do O2 meter readings and relate that to in situ growth rates.
As plants fix CO2, they give off a fixed ratio of O2.

Still, it does not tell you what the CO2 levels is.........

Regards,
Tom Barr
 

VaughnH

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one mile per hour seems to be a very slow flow velocity, but that is about 18 inches per second, which doesn't seem nearly as slow.

To relate this to water movement, consider a tank in which all of the water flows uniformly from one side to the other at 18 inches per second. I calculate that this means a flow rate of:
for a typical 29 gallon tank, 3800 cubic inches per second, or 59,000 gallons per hour.
for a typical 55 gallon tank 4700 cubic inches per second, or 72,000 gallons per hour.
for a typcial 125 gallon tank, 9100 cubic inches per second, or 144,000 gallons per hour.

A #2 Koralia powerhead moves 600 gallons per hour.

Obviously, we can't move all of the water in the tank at that velocity!!
 

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More background info:

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This explains the retention of nutrients within the beds.
Settlement of detritus is an inverse function of flow rate.

Boundary-layers around bladed aquatic macrophytes

A factor of 10 in differences by waves and other flow related drivers.
Also, nutrient uptake is discussed a lot, but little about CO2 uptake, demand, changes etc in any of the papers really.

Surprising really.

Regards,
Tom Barr
 

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VaughnH;27840 said:
one mile per hour seems to be a very slow flow velocity, but that is about 18 inches per second, which doesn't seem nearly as slow.

To relate this to water movement, consider a tank in which all of the water flows uniformly from one side to the other at 18 inches per second. I calculate that this means a flow rate of:
for a typical 29 gallon tank, 3800 cubic inches per second, or 59,000 gallons per hour.
for a typical 55 gallon tank 4700 cubic inches per second, or 72,000 gallons per hour.
for a typcial 125 gallon tank, 9100 cubic inches per second, or 144,000 gallons per hour.

A #2 Koralia powerhead moves 600 gallons per hour.

Obviously, we can't move all of the water in the tank at that velocity!!

But we can move a lot of it by using the boat propeller style reef powerheads.
18 inches a second is not much, think about it in cm/sec, then it's pretty good really.

We are not trying to deposit sediment either, which influences soil fertility and plant distribution.

So applying this is not quite what the research had in mind, but it does show how too much flow is bad and not enough causes sedimentation, algae epiphytes etc.

It also shows how aquatic plants modify their environment and greatly reduce/restrict water movement within the plant beds.

How this influences CO2, it is a real question and an area that ought to be of strong interest to researchers.

Regards,
Tom Barr
 

Tom Barr

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One of Wetzal's group did this study where the differences where 7X in CO2 concentrations from the edge to the center of the mats.

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You can also see how O2 and growth is affected as well.

Quite dramatic.
However, we do not know the current and flow, important information.
Still, as you can see, there is a large difference due to plant uptake of CO2.

The CO2 meter may be able to take many more spacial measurements of a plant bed and how the CO2 varies in complex species communities and be able to relate that....................to CO2 competition and answer why or why not a species is present, increasing or declining based on CO2.

Regards,
Tom Barr
 

VaughnH

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If you had the time and inclination you could spend most of your time doing this research, writing it up, and all of us would benefit greatly. I'm impatient to see the results!
 

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VaughnH;27885 said:
If you had the time and inclination you could spend most of your time doing this research, writing it up, and all of us would benefit greatly. I'm impatient to see the results!

Be awhile. You can still draw some conclusions about the potential results and predict, but not really verify.

Still, the expectations seem fairly clear in these old measurements.
what I find incredulous is how some aquarist cherry pick the research when it suits them, say with PO4 water column levels without measuring/even considering the plant's internal PO4 critical values, then use that as some poorly thought out argument for PO4 limitation, and without testing it, yet make huge assumptions about CO2, again, without testing.

I understand the lack of testing in most all cases for the hobbyists, however, the cherry picking of research that supports their contention is really troublesome.
I look for a good article that's well done and run across some that are not as well done, or less specific to what I'm researching.

Some cases have conflicting results and conclusions.
With Barley Straw, there was about 50% saying it worked to varying degrees, and 50% said nope, got nothing.

Looking further into methods, we see they used few controls algae bloom germination(none). So unless you can compare the effectiveness fairly across all treatments and add the right life stage of the pest(in this case algae) it's impossible to say much about how the straw might work.

This is why I first induce algae, then I test(both before and after inducement).

Often times it can take many searches for various key words or a friend mentions a paper etc, you get tired of searching etc, then come back later refreshed.

Insight takes time, at least in my thick skull. I'm stubborn, hard headed as anyone.
But knowing that, I can let the mind wander and perhaps it'll find something worth looking at closer.

The other measurement that can be looked at closer and is rarely done is O2 readings which are excellent for a non destructive plant growth rate measurement. I've been using the LDO probes and Hach meters for this. Very pricey like the CO2 meter, but..........also very accurate and easy to use.

Adding a good current flow sensor to this, now we can really see the effects of gas and flow dynamics.

I have a couple of PAR light meters, so that's covered as well.
NO3, PO4 etc are easy to measure, sediments can be sent off to the lab for analysis for relatively decent pricing.

So now you can cover about 99.5% of things that influence growth in a planted tank.

Regards,
Tom Barr
 

kevinbuckley70

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CO2 direct measurement sensor

I've just got my hands on a cost-effective NDIR direct measurement CO2 sensor & I want to see how useful it is for measuring the CO2 in my tank (this is just for fun - I currently have a pH controller, solenoid valve doing it for real!). The sensor is designed for air measurements & reports percentage CO2. I'm trying to find the formulae (in a REALLY easy to understand format!) which relates dissolved CO2 as ppm or mg/L to the percentage CO2 which would exist in a closed sample of gas in contact with the water surface (via Henrys Law presumably). Can anyone help with that? Does the question even make sense? - Regards, Kevin
 

Tom Barr

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Unfortunately the air vs dissolved does not work the same.
Using a small destructive sample run through an IR might be good, not a good in situ method really, but could be done if the water/CO2 sample was vaporized for the IR reading...............

The dissolved CO2 meter is really the tool that we need.

A good flow meter would be nice, but simply using the micro bubbles to measure and see how flow works is pretty easy, a ruler and stop watch is all you need.

I think you will find a huge difference within the plant beds vs open areas in the tank.

Regards,
Tom Barr
 

Chiya

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Hi Tom,

Don't keep us waiting, we want to look at some results =D

Anyway, I was wondering, considering a tank with good flow on the right of the tank.

Obviously, CO2 / Nutrients / Dirt is distributed well at the right side.
What about the left? Wont it have slightly higher CO2 (along with all the dirt) since it's all stuck and not moving?

Since in EI we aim to 'overfeed' our plants, isn't it be better if CO2 is done the same way? I know that gas/liquid move from areas with high concentration to areas with low concentration to reach equilibrium so mixing it around does not seem to be that much problem (IMHO)

On the other hand, I agree with having good flow as it removes dirt from plant leaves. I'm still struggling to have good flow in my tank so if there's good enough reason for me to be lazy, I would :p

Regards,
Ryan