O2 vs. CO2

[lectraplayer]

How proportional is O2 vs CO2 in relation to each other? I would assume that, for example, if I stopped my air pump causing O2 to fall (assuming it doesn't sink too far!) Then CO2 would rise for my plants to soak up. How accurate is this? If I dosed CO2 at this point, would this displace O2 for my fish? ...or would I do better to keep my air pump going and dose CO2?

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[jetajockey]

From what I understand, one does not necessarily displace the other. The biggest concern when dosing co2 is to minimize surface disturbance because it allows the co2 to offgas faster.

 

[lectraplayer]

If CO2 concentrations fall below ambient (because of the plants) how well will my tank pick up CO2 through the HOB filter and airiation?

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[schoeplein]

Primary diffusion of CO2 into water comes from fish exhalation, or liquid carbon dosing, assuming you're not injecting CO2 with a pressurized system. Using an O2 pump will accelerate the loss of CO2 in the tank by causing excess surface agitation.

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[ScotJudd]

Hi.
Turbulence at the water surface increases the oxygen absorption but de gases the Co2 but not the liquid carbon such as Excel. It's a balancing act. I have a heavily planted tank and air stones and pressurised Co2 are on timers.
7am - air stones off/lights on
8am - Co2 on
5pm - Co2 off
6pm - air stones on
8pm - lights off
I have never seen the fish gasping at the surface. Monitoring the Co2 level is key.
I add a normal dose if Excel in the morning to kick start the Carbon level with the added advantage of a mild algaecide.
Hope that's of some help.

 

[Mebbid]

It's important to note that liquid carbon supplements do not change the CO2 level but rather are a complex carbon molecule that plants can uptake rather than co2.

 

[ScotJudd]

That's a good point, Mebbid.
I use a combination of Excel and pressurised Co2. I find the Co2 can be used at a slightly lower level protecting the fish and still get good plant growth.

 

[BBradbury]

Carbon Dioxide

How proportional is O2 vs CO2 in relation to each other? I would assume that, for example, if I stopped my air pump causing O2 to fall (assuming it doesn't sink too far!) Then CO2 would rise for my plants to soak up. How accurate is this? If I dosed CO2 at this point, would this displace O2 for my fish? ...or would I do better to keep my air pump going and dose CO2?

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Hello lec...

Well, water (H2O) is hydrogen and oxygen. There's no CO2 (carbon dioxide). There will be traces of carbon dioxide from the respiration of fish, plants and bacteria that will mix with the water. It rises to the surface and dissolves into the air. CO2 is a gas at room temperature. Warm water doesn't hold as much oxygen as cooler water, about 8.2 parts per million at roughly room temp.

If you have a lot of surface movement in the tank that mixes oxygen into the water, that action will remove carbon dioxide. So, you don't want a lot of air stones and such agitating the tank water if you want good plant growth. At least that's been my observation from working with my tanks.

Sorry, that was a short answer, made pretty long. Hope that helps.

B

 

[lectraplayer]

So I guess CO2 won't enter the water unless deposited will it? I figured it would dissolve into the water like oxygen would (albeit in lower concentrations because there is less CO2 in the air than there is oxygen).

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[Mebbid]

So I guess CO2 won't enter the water unless deposited will it? I figured it would dissolve into the water like oxygen would (albeit in lower concentrations because there is less CO2 in the air than there is oxygen).

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Assuming plants and algae aren't consuming it faster than it enters then dissolved co2 will reach equillibrium with atmospheric co2 which is very very low. Other than that it requires something to add co2 into the water such as livestock and supplementation.

 

[lectraplayer]

That's what I was originally thought.

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[ScotJudd]

Just as a matter of interest, I ran my planted tank for the first 3 months using Excel as a carbon source and kept the air stone running. The fish and plants did well. This is a much easier option than pressurised Co2 but my plants did even better with the Co2.

 

[Mebbid]

Just as a matter of interest, I ran my planted tank for the first 3 months using Excel as a carbon source and kept the air stone running. The fish and plants did well. This is a much easier option than pressurised Co2 but my plants did even better with the Co2.

On a scale of 1 to 10 for efficiency as a carbon source excel rates around a 6 while pressurized co2 rates a 10. Excel works well but nowhere near as well as pressurized co2.

 

[bud29]

If you have a lot of surface movement in the tank that mixes oxygen into the water, that action will remove carbon dioxide. So, you don't want a lot of air stones and such agitating the tank water if you want good plant growth. At least that's been my observation from working with my tanks.

Not necessarily. CO2 levels are always trying to reach equilibrium with the atmosphere, and since many non CO2-injected tanks are a bit below equilibrium, surface agitation may slightly increase CO2 levels (although it won't really make a huge difference). The issue comes when the tank is actually injected with CO2. The levels will still try to reach equilibrium, but since the concentration in the tank is higher than the atmosphere, surface agitation will cause the levels to drop.

 

[lectraplayer]

On a scale of 1 to 10 for efficiency as a carbon source excel rates around a 6 while pressurized co2 rates a 10. Excel works well but nowhere near as well as pressurized co2.

Is pressurized CO2 really more efficient or does it just have "a bigger motor?"

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[Mebbid]

Is pressurized CO2 really more efficient or does it just have "a bigger motor?"

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It is actually a lot more efficient. Plants will grow quite a bit faster on co2 rather than glut.

 

[ScotJudd]

I agree with Mebbid - again. Co2 injection is far better for plant growth than Excel/Glut but it is more expensive to set up and trickier than simply dosing with a liquid supplement. Excel/Glut is better than no carbon supplement at all.