Airstone and plants?

[BillD]

This is a good discussion. Densely planted tanks can remove most of the CO2 in a tank under the right conditions, such as intense light. The purpose of injection is to increase the amount of available CO2. Since CO2 dissolves easily in water, injection works very well.In a CO2 injected tank, you don't want a lot of surface agitation which would hasten the gassing off of the CO2. So, the idea of low water movement has merit in an injected tank. In a non injected tank, if the plants use up CO2 faster than it is being produced , than, water movement will help replenish it via the surface to air interface. You can not increase the concentration of CO2 in the water above what the concentration is in the air. By the same token if you were to vigorously agitate water that has been injected with CO2, you could only gas it off until it reached the concentration in the air.
This is basically what is happening with the oceans. The high concentration of CO2 in the air is getting into the ocean water and lowering the pH. This type of occurrence is probably amplified at the shore where wave action is often intense.
I too, have grown thousands of plants (no exaggeration) in a tank with air powered sponge filters and no ferts. I can post pictures if you like

 

[aqua_chem]

Well, you may be. Since oxygen is a plant biproduct. By this I mean plants during daylight hours give off this gas. It seems to me to be counterproductive to mix even more oxygen into the water while the plants are working to remove it. I was taught if I wanted a heavily planted tank that I needed to avoid strong water movement at the water's surface.

The assumption here is that oxygen is somehow deleterious to plants. It's not, it's actually critical to plants during the dark cycle (somewhat a misnomer, as it occurs during the day as well to a lesser extent). There are environments with very high levels of oxygen that support immense varieties of plant life, such as streams. It's simply not counterproductive to maintain high levels of oxygen in tanks.

As far as the physics goes, BillD has it pretty much spot on with his description. I agree that most people vastly overestimate their CO2 levels in non-injected tanks. I seem to remember a story on TPT with Tom Barr using an electrode to measure CO2 levels in his tank, and that there was a 20-30 ppm difference between different parts of the tank based on how much exposure to plants the water had, suggesting that plants rapidly extract CO2 from water when available.

 

[candygirl415]

When I started this thread, my concern was planting on top or very near my airstone. I chose not to. However i've learned alot from all of this. I got some excel and will only dose when it looks necessary.

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[Hulka9]

Since CO2 in the tank attempts to reach equilibrium with the CO2 in the air, anything that moves water is likely to increase the amount of CO2 in the water in non injected tanks, not decrease it.

Sorry, but that is wrong... I've researched that subject and it releases more than it would add co2 to the water. Co2 just tries to escape.


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[aqua_chem]

Sorry, but that is wrong... I've researched that subject and it releases more than it would add co2 to the water. Co2 just tries to escape.

I'm sorry that you think that, but that's not the way it works in the slightest. Per Henry's Law, gases reach an equilibrium between atmosphere and a fluid based on the concentration of atmospheric CO2. If the concentration of CO2 in fluid is above this concentration, there is a net loss of CO2 from solution; if below, there is a net gain. A noninjected tank consumes more co2 than it produces (plants will consume more than fish/bacteria produce in most circumstances, as observed by rapid response CO2 probes), so CO2 will be below its equilibrium levels, meaning there will be more co2 entering than leaving.



For more reading on the matter, you should read the Wikipedia pages on Henry's Law, reaction quotients, and Dynamic equilibrium.

As far as background goes, I used to TA this class at the university level (freshman chemistry). I'm pretty confident that this is how it works.


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