I recently installed a CO2 meter: Water Management Technologies, Inc. - OxyGuard Products - Portable Dissolved CO2 Analyser

I took some readings in several tanks over a few hours and saw a wider range than many have ever suggested. I've long suspected localized areas of CO2 variation, and suggested increasing current to compensate. Many hobbyists have logn assumed that the CO2 concentrations have been homogeneous/the same throughout the entire tank.

I've long claimed otherwise.
Thus many hobbyists have still enjoyed their speculation about nutrients being the cause of all algae and plant issues. However, if we consider the role of CO2 and C in plant growth, it stands to reason that it must pay an enormous role.

"Oh here Tom goes again, claiming it's all about CO2, just add more and mircles will occur"

However, now the data using a device that can measure very accurately to within 1 ppm CO2 suggest I was right all along.

Some data on a 180 gallon tank with high light, ADA AS, good dosing and very high flow(3000 gph):

Near out flow of the filter from which a venturi CO2 input originates:

5 cm away: 40-100ppm
30-40 cm away: 20-30ppm
Within the plant beds: 8-12 ppm

Now for a 20 Gallon tank with 250 Gallons per hour flow:

5 cm from CO2 source: 35ppm
15 cm: 30ppm
30 cm: 22ppm
50 cm 17ppm
Within plant beds(dense): 6-12ppm

Note, these are just averages.

Response time is about 1ppm.

Some interfering ions for pH/KH that are common:
Ammonium, PO4, borates, hydroxides, all things that are present in most planted tanks.

This method gets around that, gives accurate fast readings
It's more accurate than the pH/KH table assuming it is correct ands all the Carbonate is Alkalinity and that the pH is only influenced by bicarbonate and CO2.

Still, this verifies, that even in smaller system and particularly in larger systems, the role of both current and CO2.

Why speculate when we can measure? Verify?
Test our assumptions and hypothesis and discard those that we cannot find evidence for?

Seems like a poor argument and method to sit around and speculate, criticize and not get any resolution. A "who can yell louder" match is a typical web debate on many such topics, rather than anything that follows a logical path to a better understanding.

I think that this meter did this job and verified what I'd been suggesting all along.
I checked the calibration a few times and it was dead on. The nice thing here is that you can quickly measure dose response effects. Add a bit more CO2, watch the meter pick up the increase really fast. The other thing is where hobbyists have been measuring their CO2, either the drop checker, the pH probe or the water sample. KH is stable throughout but pH may very well not be in relation to small(actually quite large) changes in CO2.

The meeter can be moved around throughout a day and check various spots, even the leaves of a specific plant!

I also measured 30ppm in a Discus tank and we sat and noted no differences in behavior, something I've also said for years but many discus folks have long claimed otherwise.

Then when shown this data, they back tracked and said, well, "the fish need to slowly acclimate to CO2, and get use to it over time".

Yet respiration is not like osmoregulation.
So........even when faced with such evidence, they try and weasel out of it.
One thing that shocked me a bit was just how tolerant fish are to higher levels of CO2. I'd predicted much less. 105ppm and the large school of cardinals where fine. But I find such information interesting and am happy to discard such theories when they are wrong.

The next step would be to use a current flow meter that can measure small ranges in situ along with CO2.

I'll do some more presentation of data and also bring in O2 data from the Hach LDO meter so we can compare both O2(plant growth) and CO2 demand/uptake simultaneously.

Likely the next BR newsletter.

Regards,
Tom Barr

Tom, did you see a gradient from bottom to top of the tank? Since CO2 comes out of solution as easily and as fast as it goes into solution I would expect that the surface water would have near zero concentration, no matter how much was in the bulk of the water. So, I would expect a gradient from top to bottom of the tank, with the maximum concentration near the bottom.

That should be true if the plant uptake is very slight. Add the plant uptake and the gradient would be much more complex, so I would then expect to see the maximum concentration be perhaps a third of the way down into the tank.

Now, add good water circulation........

Going along with vaughn its interesting to see a lower co2 level at the plant bed which we would assume should have the most concentration... unless the co2 even when dissolved is still rapidly moving towards the surface of the water. Does this then lend to the idea that our outputs should be closer to the substrate and not the tops of the tank?



Whis this said what type of gradient did you see? Was the co2 concentration diminishing significantly over time in a given area?
Not to sound silly but if you had a tank of blue marbles and put red marbles on top wouldent it take mixing action to get the red marbles distributed throught the blue marble tank? Shouldent this then also be true for H20 which is just a bunch of marble molecules?



btw, thanks for spending your hard earned cash to further the developement of knowledge of aquatic plant systems.

I believe it means less circulation between the more leafy areas just by virtue of the mass and thus less co2 getting there from your reactor due to restricting the flow...

A tank is needed that is built like a whirl pool tub. Multiple intakes on one side and the same returns on the other side. Direct flow through river style. Such a tank probably wouldn't be visually pleasing but the flow problem might be taken care of.

Don't forget the reason why we put CO2 in the water - for the plants to consume. And, because plants are largely made of carbon, they have to consume much more CO2 than NO3, for example. Just the consumption of the CO2 would account for some or maybe a lot of the variations. That is subject to being calculated, making some assumptions. I'm sure Tom has the data, theories, equations, etc. needed to make such calculations, but I don't.

Like a lot of really simple subjects, this is only simple until you know more about it. I think some really interesting information is coming along pretty quickly!

No kidding! I added a Koralia 1 to my 72 gal and it's helped a lot but did not seem to have enough GPH flow overall. A friend had a used but good shape Koralia 3 at a good price so I got it. I put it in my tank it was like a friggin' blender in there! My SMS was moving, the plants swaying everywhere, some even came up out of the substrate, the fish were like, whoa, what the heck! I tried moving and pointing it in different directions but it was still like Dorothy in the tornado scene of the Wizard of Oz. The Koralia 1 is rated at 400 GPH, the 3 at 850 and that's just too much (but man what good CO2 distribution I'd have!). So now I'm thinking to find someone who might want to trade their Koralia 2 (rated at 600 GPH) for my 3.....

I use the model 2 on my 45 gallon tank, and I think it is perfect for that size. I also just noticed that Drs Foster& Smith have them on sale now: Water Pumps & Wavemakers: Hydor Koralia Water Circulation Pumps

I just reset up my 45 gallon tank, to be run with lower light and mostly low light plants. I put the Koralia on the right rear side, with the flow directed along the back wall. My filter outlet and inlet are in that same area, with the filter outlet flow going diagonally towards the left front corner. I have no plants in there yet, but it looks like the flow pattern will be good. In any case the fish are enjoying it right now.

No offense given Vaughn or taken I hope.

The flow issue seems insurmountable and dead zones may always be somewhere. Even Tom admitted that he was surprised by some results and look at all the experience he has. Then you have those of us who have been lucky enough to gain from his and others knowledge. I don't make light of this subject at all and look forward to the outcome.

I'm not the least bit offended. Maybe my enthusiasm for learning some more about planted aquarium keeping, something I think will be extremely interesting, is making my comments read differently than I mean them to.

I have always considered water circulation to be a side issue - just add a powerhead and forget it. And, I believed, as so many did and still do, that the concentration of nutrients in our tanks was virtually uniform all over the tank. I heard Tom tell us that wasn't the case, but just chuckled to myself with a "there he goes again" attitude. (I felt that way about light intensity too, until he showed me the readings with a PAR meter in a tank.) That's what I meant by viewing the circulation subject as a very simple issue. What really makes me chuckle now is the memory of when planted tanks were so simple to me - put sand in a tank, add water, add some plants, sit back and enjoy the tank.