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.

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?

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.)

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.


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

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?

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

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

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Wiley InterScience :: Session Cookies

http://www.cosis.net/abstracts/EGU20...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

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.

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.

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,

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