Where does the CO2 come from in nature?

[WhistlingBadger]

Greetings, fish lovers.

I have been using flourish excell in my 55g, and while it seems to have wiped out my cabomba and anacharis, it is *great* for my amazon swords.

Now, it seems to me that a good tank is all about re-creating nature in a semi-closed system. Everything that happens in the tank--food, aeration, filtration, water changes, et al--simulates, recreates, or replaces something that happens in nature. The challenge of making that working mini-ecosystem is a big part of what I love about fish keeping.

So, in dreaming about some new and interesting ideas for biotope tanks, I have been pondering this whole CO2 thing for a while. What is the cognate of CO2 augmentation is in nature? Is it natural aeration (and if so, why doesn't that work in the aquarium?), fish respiration (ditto), some decomposition process, or what?

I like to know the theory behind what I'm doing, instead of just paint-by-numbers. It drives me crazy sometimes. Anyway, thanks in advance for the insights.

Tom

[mizzoutank]

google the "walstead" method.

That'll be the only real way to go as natural as you wish and or it'll lead you to how the co2 is created in the wild.

[Limming]

My theory is that in nature CO2 comes from fish breathing (along with other things). The reason this doesn't work in aquariums except for low tech tanks is the amount of plants in a aquarium is simply a lot more in small area than in nature. This means that CO2 is much more rare in a tank.

[talldutchie]

Which is why the average biotope doesn't look much like an aquarium.

[Brhino]

CO2 also comes from gas exchange with the air in nature - I'd wager that's a more significant source of it than fish respiration, especially given that some bodies of water are too small to support fish but still grow aquatic plants. It's just that people with high-tech, heavily planted tanks have an unnatural concentration of plants with an unnatural desired growth rate.

[homemadepopcorn]

+1 to Brhino... there are also microorganisms that utilize oxygen and respire CO2 which aren't necessarily in aquaria. I've read that the concentration of CO2 in water bodies in nature tends to run higher than the concentration in the air although I don't know how true this is.

[talldutchie]

I suspect that may well vary an awful lot.

[dmagerl]

CO2 concentration in water will naturally come into equilibrium with the air at around 3ppm. I've seen numbers posted that suggest that with fish respiration in our tanks, that number increases to around 6ppm.

In nature water can be naturally carborated by the mineral beds it runs over. A stream with a limestone bed can have a significant amount of carbonate and hence CO2 just from the limestone dissolving into the water.

Another thing, I've seen comments that most underwater plants grow in water that is significantly less clear than the water in our tanks and at greater depths. Thus they receive less light than what we provide over our tanks and hence require less CO2 for growth.

[madagascariensis]

plants in nature don't look like plants in the aquarium. I've been canoeing in northern canada and seen youtube videos of aquarium fish in tonly have their bottom parts submerged(most aquarium plants actually are mostly emergent). vibrant algae free growth of actually emergent plants is somethings aquarists create with CO2 and specially balanced fertilization schedules and light intensities. you are right.
all of these factors are present in nature but in order to create a more satisfactory display for the aquarist him/herself theyare augmented or certain ratios are artificially increased.

[Gogi]

I do not believe you can ever make a self sustaining natural aquarium unless you can provide water flow with out using any electrical devices. Even the walstad method requires filters. This is a great thread. I have also chewed on all these questions from time to time.