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Re: [APD] CO2 in the mist

Hi Terry,

>Jumping into where only fools may dare................can you see with your
>eye the difference in the size of a swirling bubble that has 0.03%
>inerts/non-CO2 vs. 0.001% inert/non-CO2? I wouldn't try.

Neither would I. Them bubbles are quick. 

>I proposed to Tom that he consider using an extremely efficient diffusion
>device that will highly saturate the water with CO2 - but no bubbles and
>make the comparison that way. This may actually tell more about whether the
>presence of bubbles actually does something more.

Already have done this and have done it with the external vs interal versions of the CO2 reactors I've made and sold to many folks here. Old stuff I have already long considered.
I've been wondering about this for a long time. Plants do not lie and I've seen the differences between both the methods with the internal CO2 venturis vs the externals.
I recently developed an external venturi, pretty cool.
Knocked Mike's 180 gal CO2 problem from hell to the good range with no other adjustments by 0.3-0.4pH units. Pearling now starts about 3 -4 hours earlier. I have not gone after it with a DO meter, but he does not care, the tank is doing much better and the algae stop growing.
I've made nearly a dozen designs over the last 12 or so years. 
I have 100% of the gas in solution that is dosed for the tanks.
I've made all sorts of reactors from 1 gal to 2000 gallon tank sizes and tested them for effective usage(zero bubbles from the outflow and response times to pH drops).
I've done this method for many years, many folks have, it works well when the CO2 is near 30ppm. We did not see CO2 issues till folks started adding more light(the light was not available back then generally unless you where a DIY'er or wanted to spend the $ for MH's(I did).
 My point with the gas CO2 mist, is that it definitely increased O2 levels in the tank versus the other methods. This is a standard method to measure and to quantify aquatic production(O2 evolution) in the aquatic sciences. 
While pearling/growth rates are the more "practical things" many aquarist use to see and gauge their tanks, this is a bit more clear when making comparisons about whether growth is increased using say one method vs another for CO2 injection. CO2 is also a large % of uptake and resources for the plant.
The tank is still jamming along, everything look Riccia with the pearls, DO levels are sky high. 
 No water changes yet.  You do get good CO2 levels and growth and DO, but I've gotten roughly 25% more O2 using the misty bubbles method.  I need to run more repetitions though. The initial results do look good. 
We'll see as time goes on. 
Folks typically are unwilling to blow 300$ or more for a DO meter.
Some places make cheaper ones these days but they still ain't cheap. Test kit versions typically do not go beyond 10ppm but are relatively cheap.
>I can imagine that the bubbles are providing very high CO2 levels at the
>leaf surface where they may touch (do plants have specialized cells on their
>surface that may just suck that CO2 right up? - I don't know...need to look
>it up)....or that there is a very CO2 enriched water region around the
>outside of the bubble that they similarly enjoy.

Since the pure gas bubble is under the leaf where most plants have their stomates, the distance is minimized. All cells take in/expel O2/CO2 etc in aquaeous form (even us in our lungs). 
The rate is determined by Fick's 1st law of diffusion.
A distance(1), diffusivity(2) and concentrational gradient(3) are the main variables.
1. Adding CO2 mist reduces the distances(minor/not significant)
2. Gas vs a liquid. Clearly the gas can move faster (large factor) 
3. Increases the concentration (probably the main factor).
These are the main mechanisms.
No one mentioned these.
The other issue, few folks have ever studied this notion of misty CO2 in nature.
For all I know, I am the first to suggest it. I have never seen anything about it in the research(gas mist vs dissolved CO2 etc).
This mist adds lots of rapid contact(even if pulsed) for the plant cells(they can store a little bit of reserve fixed CO2 and it also diffuses in the cells internally).The same is true for other nutrients. Stomates are the generalized name for the openings and guard cells are the cell types that take up CO2 and expel O2. Some aquatic plants lack stomata and guard cells, eg Hydrilla. Only one plant species (terrestrial) has none, and many of the plants we keep are amphibous(and have them).They are generally on the abaxial side of the leaf, (the underside) but Water lilies have them on the top and a few other plants have exceptions.
The CO2 in these plants diffuses directly into the cells, they do not need to transport CO2 further since the leaves are 2 cells thick. Water lilies have floating leaves and would not do well to have them on the lower side and they do not need to worry about water loss unlike terrestrial or amphibous weeds.

>but come up with another
>test that can tease out what may be going on here. Certainly it's not a
>character issue.
>What do you think?
>Terry Barber

Well, there are reactors that dissolves 100%, they are available and have been for a long time(now they are much more reasonably priced). The diffusers have been as well, and the venturi design I've sold years ago and used for nearly 12 years has been around.
The main gripe was the thing was in the tank.... even though it's more user friendly and preforms better in terms of O2 levels. I have no issue addressing the method of O2 as way to measure growth in Submersed aquatic plants or algae. 
Explaining why this occured was more elusive even though it seem like it was wasting gas was less obvious.
Re-examining the concentration/gas phase transfer and direct absorption into the plant rather than the water first, was the answer.
Seems weird initially. 
But so did adding PO4 way back when.
Plants don't lie though. 
FYI, for folks interested in trying this at a larger scale:
These are relatively cheap and placed on the bottom of the tank's gravel (where they belong out of sight!), by placing a spray bar down low along the back wall of the tank and placing this in the way, the micro bubbles will go all over the plants. The only thing you see is the CO2 line going into the tank.
So simply attach the CO2 line to the spray bar to hide it.
If you use a sump, use the overflow box to hide the line.
The problem with filters, powerheads etc,(they burp and blech out large bubbles as well as smaller ones) is they do not produce the fine bubbles that a good diffuser will so you have less dispersal and contact time. Smaller bubbles means that you can more evenly distribute the bubbles and they are less affected by buoyancy. 
If they dissolve, you add more, but be careful, make sure the fish are okay. I have not killed a fish to date using CO2. I have killed shrimp:) But they taste so good. 
The real issue though is getting your current right.
Most folks could use some improvement there. 
Hide the ugly stuff, make the flow pattern better through the plants etc.
This will be the biggest user issue doing this.
The other user issue, the distance the CO2 travels up before it hits the current.
I placed the disc and the venturi right at the current input so that it is immediately blasting the pure CO2 all over.
3. When paying around with CO2, be careful, it can kill fish and shrimps. If you monkey with it, make sure you are around during the time you adjust it. Do not wonder off, do not go to work after setting it in the morning. Wait till you have some time. Then watch. Be competent. 
Refer back to the mechanisms also in Fick's 1st law.
Smaller tanks will have little trouble.
Larger ones might consider the large flat stones above and better flow routines.
Tom Barr


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