We have had a brief interesting discussion on APC about the effect of water circulation on CO2 distribution in an aquarium, and whether plant mass has a strong effect on it. We can all conjecture about it, but until we have a meaningful visualization of such a system it seems it will just be conjecture. So, I propose that one of us with some time, a spare tank, some spare plants, and the ability to set up a CO2 system and water circulation system for that tank do a test. This would consist of first testing a tank with only water in it. Assuming a canister filter and spray bar is used, inject a dye into the water line to the spray bar and video record the appearance of the water to see how mixing occurs. Of primary interest is how long it takes to get reasonably uniform color throughout the tank.

Then add a lot of plants - even plastic ones would work. Repeat the test.

Then, to get gaudy, repeat with real plants and CO2 injection with an external reactor and use pH reagent as the dye, watching to see how the pH varies with time all over the tank.

Too bad I left High School in 1954 - I could use this for a Science Fair project.

Wouldn't pH reagent harm the plants?

I do not know what was said at the APC nor will I go there to see.

However, as it stands and seems, I have done measurements to this extent in aquariums and in natural systems. In a typical plant bed in the Santa Fe and Ichtucknee Rivers in Florida, we found 90% reduction in flow rates inside the plant beds vs the external adjacent areas. the outer leaves had a boundary layer approximately 20X smaller than the internal leaves 20 cm within the bed.

Vertical distribution patterns also had profound impacts.

Gas exchange differences between plant leaves in these locations varied by 65%.

So if you assume a reduction by 65% of most of the plant biomass in your overgrown vs well pruned tank, there's a huge difference in CO2 demand and distribution. where you measure the CO2 is also radically important. It was rather low inside the plant beds as was O2, it was higher for both outside on the outer fringes. However, aquarist assume that their CO2 is the same and homogenous no matter what the growth stage or plant biomass.

But what the heck do I know?

There's a lot of research about this topic.
Of course conjecture is the favorite past time of many aquarist rather than research

Regards,
Tom Barr

This confirms what I posted, minus the evidence, on APC. But, of course there was disagreement. The gist of the "other side" is that it isn't believable that in such a small tank of water the water would not be the same everywhere in the tank, and the plants are too flimsy to reduce the circulation by much. I don't like being too adament about subjects like this without evidence to back me up, so I proposed the visual test to see if one of the budding scientists in the group would try it.

Carissa, this would not be an experiment for a tank of valuable plants! Any dye strong enough to show the circulation well would almost certainly be harmful to the plants. And, it would take numerous tries, I suspect, before a good test run could be made. Lots of work, emptying and refilling the tank between tests, cleaning the canister filter, etc. But, wouldn't it be fun?

I like the idea of using the ph reagent and watching the differences in ph within different areas of the tank. That would be very interesting to see. You might be able to actually see the places where co2 was being consumed. I would love to use dye on my tank and see what exactly the flow is doing in there. For now, I have to look at the co2 bubbles from the diffuser.

I'm just sorry that I dont have the resources to do tests like this one.

I would tend to think that even though the tank is much smaller than in nature, that there would still be differences in flow, co2 distribution, etc., albeit much smaller differences. I can tell that untrimmed plants certainly block flow and co2 distribution in my small 29gal. tank. I can see evidence in the growth of the plants and the presence of algae.



-Mike B-

Obviously I picked up a few o2 meters recently. At one time I had 5 probes in my show tank in the process of calibrating and testing all of them.

It was interesting to track the Co2 distribution in real time as the Sea Swirl wave generators bounced it around the tank. By the time you factor in the PH meter and the Redox/Orp you got a real eye opening experience of Co2 dynamics at work in a Real Time environment. It was as if the tank was inhaling and exhaling as Co2 rose, and o2 declined. The Orp was most useful as you could witness any excess of Co2 This actually allowed me to trim my Co2 consumption, and almost Double my saturated oxygen without even switching on the o2 reactors or Ozone.

We are at 5700 ft. so our ambient o2 is appx 13% lower here, yet the show tank is averaging well over 9.5 ppm o2 at night without any artificial addition of o2.

The wife's 50 gal. tank looks like a Tarzan movie...Very Heavy planting, and while this really screws with Co2 distribution she's pushing over 900 GPH or 18X circualtion, and her Co2 consumption stays conspicuously low while maintaining 35ppm ambient Co2 levels and o2 rarely drops below 7ppm at night. technology occasionally pays off ! LOL. Prof M

Why not just put CaCO3 in your tank and watch it. It isnt very soluable in the beginning and you can use it as GH-booster at the same time.

In addition, why use PH reagent? IF you have flow, the water WILL continously equilibrate CO2.

Well, much like the past debates with several folks there, many of the debates where minus the evidence and support
Plenty of skeptics and folks bad mouthing but few problem solvers or people offering up real support. But what do I know?


What? You did not conform? "Belief" was not good enough of a standard for you oh ye of little faith?

There is another level of scale here as well, the boundary layer level which is in the micrometer ranges.

Flow effects that greatly as well.
Yourself and many have heard me squawking about good current, even Dupla's Optimum aquarium mentions this going back into the mid 1980's. Plenty of research and support here.


Actually Methylene blue is fine, same with permangnate. Just do not add more than the suggested amounts.

Still, you need a very accurate flow meter to measure such differences.
You also need a method to measure plant growth/production in these areas.

Dyes alone will not answer the question basically.
CO2 mist is based more or less(how much?) this flow current idea also.
You can watch the mist float around and improve current that way and see the dramatic effects as you tweak and manipulate the flow.

It's might be due to the gas phase hitting the plants, or the improved flow of current. I think it's a bit of both.

Still, current explains some of the effect and this can be seen locally nearest the CO2 reactor output etc, reduce the current down sometime and test this.

You'll see better growth and more pearling in those regions even though the CO2 pH/Kh test measures the same in most places. Plants consume and assimilate CO2 as we add it.

This is the assumption many folks make(it's homogeneous) about CO2 etc.
We can have 30ppm and fish at the surface in some tanks and other can have a high fish load and never have them at the surface etc as well as excellent plant growth.

Still, think it's not important?


Regards,
Tom Barr

My evidence for the importance of current is that when I set up a tank with freshly planted plants, limited plant mass, good CO2 and good current, I don't get BBA. But, as the plants grow in response to those good conditions and I don't do any pruning I soon see BBA starting up, even though I still have good CO2 according to my drop checker. Since BBA tends to start when there is inadequate CO2 in the water I have to conclude that something is preventing the CO2 from reaching all of the plants. When I add a powerhead to get more circulation inspite of the plant mass, I have better control over BBA - for awhile - the plants just keep on growing. If I prune heavily, and maintain the plant mass about the same all the time I don't seem to get BBA. All of that suggests that the heavy plant mass interferes with water circulation, as well as consuming more CO2 in the vicinity of those plants. This isn't absolute proof that good water circulation is essential, but it is certainly very suggestive.

Then of course "John Doe" points out that he uses 10 ppm of CO2, never measures it, just uses a bubble per second in his 75 gallon tank, doesn't worry about water circulation, has 5 watts per gallon, and doses fertilizers once a week if he remembers, and posts a photo of his beautiful tank. (An exaggeration, but not by much.) It is still fun though.

I put calcium carbonate in my tank (to raise GH and KH) and within about 5 minutes the whole tank was just a translucent milky white color. It was pretty hard to see much of anything. Though at first it was kind of fun to watch.