CO2 Gas Exchange at Water Surface

[mohican]

So this has been bugging me... I've been told that it is possible to keep a lush planted tank without adding ANY form of co2 to the tank. The gas exchange at surface is enough. What is the truth behind this statement? If it were 100% true none of us would use co2 supplementation, right? Most of us here add it somehow and we have some pretty sweet tanks I'm interested in everyone's thoughts.

 

[aqua_chem]

You're not going to be able to get nearly high enough of a CO2 concentration with surface agitation. Even in nature, I don't believe that atmospheric CO2 plays a large role with aquatic plants, but I might be wrong on that.

 

[mohican]

That's what I thought. I didn't want to argue with a "know it all" so I just moved on. I had to post it to get some real thoughts from AA.

 

[Florio]

That's what I thought. I didn't want to argue with a "know it all" so I just moved on. I had to post it to get some real thoughts from AA.

Uhm the only way I know of that you can pull off no co2 is with a dirted tank.

 

[aqua_chem]

I've grown plants without CO2 or dirt before. It's more of a question of practicality than possibility.

 

[Florio]

I've grown plants without CO2 or dirt before. It's more of a question of practicality than possibility.

I've really never looked into it, but I've looked up dirted tanks and apperantly your plants grow better than with a gravel or sand + co2.

I imagine with just gravel or sand you couldn't have too many plants cause of co2 demand.

You could probably do a few plants just fine?

When I first started I grew some plants in my gravel with no co2 or fertilizers but I only had one and it didn't look like it was in too good of shape but never the less it did grow.

 

[jetajockey]

You can grow a densely planted tank without supplemental co2 or dirt. The plants will limit their growth based on available carbon but many will make do by stripping carbonates from the water. The dirt is primarily a nutrient source, so it's role in co2 supplementation is minor, if measurable at all.

The biggest factor is to have an adequate amount of light to maintain healthy growth while limiting the light to avoid a big imbalance because of the lack of co2.

 

[mohican]

When I first started planted tanks I didn't use anything and some of the beginner plants did OK. I feel they can grow, but not thrive like we envision our tanks to look.

 

[phin]

You can grow a densely planted tank without supplemental co2 or dirt. The plants will limit their growth based on available carbon but many will make do by stripping carbonates from the water. The dirt is primarily a nutrient source, so it's role in co2 supplementation is minor, if measurable at all.

The biggest factor is to have an adequate amount of light to maintain healthy growth while limiting the light to avoid a big imbalance because of the lack of co2.

JetaJockey has a valid point. Its all about the available carbon in the water, CO2 is just one source of carbon, which is why people supplement with glutaraldehyde; carbonates & bicarbonates are another source.

In a sufficiently planted tank with adequate lighting and nutrients, but no CO2 injection, the plants will use all available CO2. A change in CO2 concentration will influence the concentration of pH, bicarbonate & carbonate. Since the water in the tank is constantly striving to maintain equilibrium, as CO2 is removed from the water, the carbonates and bicarbonates present will reequilibriate, producing more CO2, thus maintaining equilibrium. Acid sources (nitric, uric, humic) help to drive equilibrium. By constantly maintaining adequate KH, one can provide a constant carbon source for plants. However, you would want to be wary of "feeding" your plants baking soda, as it is sodium bicarbonate, NaHCO3, and will break down, leaving sodium ions in your tank. High sodium levels are not desirous in the planted aquarium. If you want to feed your plants carbonates, try potassium bicarbonate, KHCO3 (sold in wine making/home brewery stores), which is actually a perfect buffer for the planted tank now that I think of it.

 

[aqua_chem]

Ok, several things.

Plants will actively use bicarb, not just CO2. This process is independent of the carbonate-bicarbon-carbonic acid-CO2 equilibirum process. Plants vary in their ability to utilize CO2, with many of the traditional 'hard water' species being much more adept at it, eg valisineria.

If you think about it, your argument implies that injected CO2 is unnecessary as long as KH is maintained above 0, which can easily be demonstrated to not be true. Your chemistry is not incorrect, but that just tells us that it's either more complicated than that, or it doesn't explain the process fully.

Second, sodium itself isn't bad for plants, as it's extremely common in nature. It's when you dose it in high amounts that TDS increases, which causes problems for plants. KCl will do this just as well as NaCl will., but is used less for practical reasons.

 

[jetajockey]

I read a mile long thread on carbonate stripping vs injected co2 a few weeks ago and from what I remember, the co2 gleaned from the stripping process is not as efficient as injected co2. Also certain plants can do it and others cannot. So it helps, but only to a certain extent. This helps explain how we easily see 'too much light = massive algae" scenarios in tanks without co2 injection.

That's my dumbed down recollection of it anyhow

 

[mohican]

I knew plants can use the co2 created in the tank and that amount was limited, but this must got real intense (lol).

 

[phin]

Ok, several things.

... Your chemistry is not incorrect.....

AquaChem says my chemistry is right!

 

[Oohitsae]

I grow my plants without any kind of co2 or dirt, I don't even add fertilizers
co2 is only necessary in high light tanks and usually it's just so people can combat algea
The tank in my avatar has a ton of low and moderate light plants, in gravel and they all do just fine. Don't grow as fast as they would in a tank with co2 but still grow at a good rate.
I should add, I haven't read all the other posts yet so I apologize if someone has already said that

 

[mohican]

So is it safe to say that in order to have lush plants they must be fueled by something; either CO2 or carbonate dosing? Having a tank with nothing going in will starve the plants growth correct?

 

[phin]

So is it safe to say that in order to have lush plants they must be fueled by something; either CO2 or carbonate dosing? Having a tank with nothing going in will starve the plants growth correct?

CO2 will diffuse into the tank from the atmosphere, but this amount is minimal. Your water also has some level of carbonates in it already (unless you are using RODI water and not buffering). Plants will grow without any carbon supplementation, just slowly, and limited by the amount of carbon, which will mean you need to limit the intensity of your lights and amount of nutrient supplementation as well, since the plants' usage of these will be limited by the amount of carbon available.

 

[mohican]

That's just what I figured, thanks for the brief summary phin.

 

[aqua_chem]

Conservation of mass. The plants have to be getting their building blocks from somewhere, its just a matter of from where and how convenient that source is form that plant.

 

[mohican]

So to have CO2 diffuse into tank naturally, does the top need to be off? The exposed surface area of the tank would be minimal with glass top on correct?

 

[phin]

tops aren't air tight. Openings for filter tubing are sufficient.