I don't mean the obvious reason, they need a source of carbon. I mean, don't these plants live in the wild somewhere just fine, without co2 injection? If so, why do so many plants seem to require this in captivity? Obviously there are a vast range of things that are different, I'm not trying to say that we are really recreating nature in a glass box. I'm just wondering what it is in particular that is different in captivity that generates the need for co2 injection for some plants. Or are these plants so different from the plants in the wild now that they have different needs?

I'm guessing the main reason for injected CO2 is speed of growth. I made a small (10G) non-CO2 tank a while back and have been experimenting with different plants. Everything I have put in there has grown and all are healthy looking: anacharis, anubias, java ferns and mosses (all expected), but also crypt wendtii and corkscrew vals are doing rather well (unexpected) and spreading. Speed of growth, however, is multiple times slower than my CO2 tank, which I'm sure would tax the patience of some planted aquarium folks! I'm guessing it would take quite a while for a non-CO2 tank to "fill in" with plants. For a non-CO2 tank, Tom has recommended using a liquid fertilizer (CO2 type) to help the tank grow in, in the beginning.

One thing I should mention about my 10G non-CO2 is that I have 2 of the bio-wheel type filters on it (250gph total!). There is quite a bit of turbulence and air bubbles are constantly flowing down to the bottom of the tank. This may give me a little more CO2 ppms than the average non-CO2 tank, I'm not sure.

Anyway, I'll keep throwing plants into my non-CO2 tank and see if they grow ... some of them look a lot different (stringy stems or smaller leaves) ... it's a fun experiment.

As far as plants that simply will not grow without CO2 injection, I'll leave that question to an expert. Besides, I haven't found a plant that won't grow in non-CO2 yet. One of the biggest issues with plants not growing in a non-CO2 tank would probably be too little light, since we keep the light on the low side to avoid algae.

Yes, I think it's we need not the plants, lol. Suppling CO2 as a nutrient to increase growth beyond that we can find in nature. Purely selfish on our parts. but fun

In line with Ted, I also maintain 2 non-carbon tanks. For fun when I get a new plant I throw a piece or two in to see what happens. Rarely, I must go back and retrieve the piece to try again in the high tech tank. Everything I've tried in the non-carbon tanks survives and grows, just slow. These tanks are incredibly stable and take very little care.

There are many places where the CO2 is quite high in natural systems.
Plants often go right for the surface as well to get it.

Others use bicarb etc.

Some slow their growth, some use CAM etc.
My site was 25 ppm of CO2 in the Ichentucknee springs.

CO2 rich ground water is how caves are formed.........and peat formation on limestone is also not a bad way either.

So CO2 varies a great deal in nature.

Regards,
Tom Barr

That makes sense, and it's probably true that most plants eventually grow emerged in the wild, we are the ones forcing them to stay totally submerged for the most part.

Also I didn't think about the fact that we are trying to maintain a virtually algae-free environment at the same time - probably most places in nature are far from that.

Take a look at the plant fest pics, wide range of conditions, algae are often transient, they live for a few months, weeks etc, then do not reappear till next season.

Adding CO2 is very much like adding as some like to call it "Excess nutrients".
Yet few folks very CO2 the same manner as they might for NO3

Well, where does it all start?
Light, then CO2..........non limiting CO2 is no different than say non limiting NO3, PO4 etc, yet I get poo pooed all the time for suggesting higher levels of NO3 when folks add CO2...........

It's common sense, not any magic leap of faith, intellect etc......

I read page after page of mumbo about how good excess high "unnatural" amplified CO2 is and how it stabilizes things in the aquarium with plants.
The same could be said for consistent dosing of NO23, K+ etc.

If you look and ask, what kills more fish in planted aquarium statistically speaking than any other single factor?

CO2.

Even heard to definitely fish kill or shrimp kill due to NO3?

I've done it, it took 160ppm+ to do so for amano shrimps.
Fish where fine.

If folks are concerned about risk at higher amplified industrial growth rates, then they should start at the source, light, then follow with CO2.

Not starting with the smaller players like NO3 or PO4.

It's just that it's popular to promote CO2 enrichment, and to poo poo higher N and P levels, research and semantics are often twisted to fit such pre drawn agendas.

These clowns cannot put 2 and 2 together.
Then try and debate me about it without ever getting the big picture.
Some are easily confused by other folks and then eventually get it when explained more clearly.

The reality is harder to understand generally than the nice furry claims, so debating against that is not always easy, but with some common sense, some simple test etc, some background checking, you can wade through and learn something.

It's a good topic about CO2 enrichment and whether we should use it or not.
It is also the least understood and the most poorly tested parameter relative to the others.

Regards,
Tom Barr