High Levels Of C02 And Oxygen

[russellbrooke]

As it's been really hot, I’ve added an airstone to the tank and moved the outlet from the pump so there is more movement to aerate the tank as much as possible. From what I understand, hotter water means less oxygen so I’m trying to make sure my fish have plenty of oxygen.

This got me thinking, can you diffuse co2 and have a well oxygenated tank as well? I'm not really sure if they're mutchelly exclusive? I want high co2 levels for my plants, but also want high oxygen levels for my fish. What's the best way if any?

Russ

 

[craynerd]

Haha, that’s a good question.

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EDIT: Sam, a few posts below pointed out i completely read the graph wrong which actually cocks up my who theory! It seems likely now that a temp of 35+ would cause a stressful oxygen level. BUT this still true....wouldn`t a temp of 35oC+ be stressful to most freshwater fish anyway!! I will leave my error in the post so as not to disturb the flow of the thread.
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The solubility of a gas decreases as the temperature increases. So you are quite right, when it’s hotter the solubility of oxygen in water decreases. Now, the question arises, is the solubility decreased that much that it is necessary to add additional oxygen to the tank for the fish in the form of an air stone? If this is true, surely the tank must be at such a high temp that it alone is distressing to the fish?


The graph i found on the web below shows that at 30oC there is still 14.5mg/l of dissolved oxygen. I may be wrong, but i am sure O2 levels of about 5mg/l become stressful to fish, so the temperature would have to be very high.

I am just speculating! I have had no experience in such a situation, but that’s my belief without a test to prove it.


Regarding your next point, having a CO2 and O2 rich tank.

Of course, there is only ""room"" for so much of each gas to be dissolved in the water. Naturally, by increasing one you will directly reduce the other by forcing it out of the water. The best you can hope to achieve would be an equilibrium between the two.

I am no expert on this, i just did a bit of research and reading around the question so if anyone has anything different to say, please speak up and gracefully correct me!!

Chris

 

[BHornsey]

Hm, my understanding is you add CO2, coupled with sufficient light, to improve plant growth.
The plants then produce oxygen as a by product of photosynthesis.

Providing your tank is sufficiently planted and lit then there should be sufficient oxygen in the water column from the plants. At night, when photosynthesis halts, the temperature normally drops (except at the moment - God awful at night just now!!!) and fish tend to rest so the oxygen demand isn't so high.

If you use an airstone or over agitate the surface you will drive off the CO2 you added to the tank.

Brian

 

[craynerd]

This got me thinking, can you diffuse co2 and have a well oxygenated tank as well? I'm not really sure if they're mutchelly exclusive? I want high co2 levels for my plants, but also want high oxygen levels for my fish. What's the best way if any?

??

 

[Themuleous]

Are you reading that chart right? I make 30c equal 7.6mg/l oxygen?

 

[craynerd]

HAHA lmao....it was a test....honest!!! Just checking you were paying attention!!!! Obviously Well done Sam, you pass and win a prize,, if u keep stum.

Which completely craps up my theory....lmao. If 30oC is only 7.6 mg/l then yea i am sure ur right, think 35oc must be well approaching a stressful 5mg/l mark!!!

GET THAT AIRSTONE BUBBLING !!!! lol

sounds like a good reason to stick to plants and forget about fish to me

Chris

 

[dasmall1]

This got me thinking, can you diffuse co2 and have a well oxygenated tank as well? I'm not really sure if they're mutchelly exclusive? I want high co2 levels for my plants, but also want high oxygen levels for my fish. What's the best way if any?

Are you asking if they're inversly proportional? (haha, is that how you spell it? ?

 

[Themuleous]

BTW I think I'm right in saying that the CO2 and O2 levels in a tank can vary independently, so would think in theory you could have both at high levels.

Just out of interest, with all the hot weather we've been having my work tank has gone up to 35C and the fish seemed fine, no obvious signs of O2 deficiency.

Sam

PS - you're secret is safe with me Chris

 

[craynerd]

BTW I think I'm right in saying that the CO2 and O2 levels in a tank can vary independently, so would think in theory you could have both at high levels.

would love to hear if this is true. I didnt think it was hence why you can drive off CO2 from the water during lights off with an airstone. I took this to be due to oxygenating the water, is it to do with the physical disturbance of the water?

Chris

Maybe your right, i found this:

http/www.thekrib.com/Plants/CO2/night.html

Remember, there is no relation between the amount of O2 and the amount of
CO2 in the water (within reason).

I`d like to know what "within reason" means!

 

[Themuleous]

I took this to be due to oxygenating the water, is it to do with the physical disturbance of the water?

As far as I know its due to the increased surface agitation and not the O2 itself. If you think about it, the air you are bubbling through the tank is the same as that is all around the tank anyway so the water and air will already be in equilibrium re the O2 so bubbling more through it aint going to add more O2 to the water.

The bubbles breaking the surface however are constantly replacing the surface water with water from below. Its probably called something like the barrier effect or something but basically when you add CO2 to the tank you create a concentration gradient from the water to the air and so the CO2 will escape the water and join the air. This process will reduce the CO2 concentration in the very thin layer of water that adjoins the air, the bubbles just constantly replace this depleted layer with water from below that contains more CO2, and in doing so maintains maximum CO2 diffusion out of the water and into the air, thereby lowering the CO2 level faster than if the tank was just still with little or no surface water movement.

Well thats what I would have thought anyway, thats just out of my head, got no proof!

Sam

 

[russellbrooke]

Well as usual, great posts. Quite a lot to take in, especially if you start reading the link from Chris. Good link btw.

When i said, "I'm not really sure if they're mutchely exclusive?", i meant i wasn't sure if you could have high co2 and high o2 levels at the same time. Maybe you could only have one or the other.

And it would also help if I could spell, mutually and not mutchely!

Anyways, thanks.

Russ

 

[zig]

CO2 will not displace O2, you can have high or low levels of both.

For the OP........there is a growing school of thought that sugests that running an airstone whilst runing CO2 is benificial to planted tanks and will have very minimum effects on CO2 levels, anyway CO2 is cheap just up your bubble rate if you run an airstone.

 

[craynerd]

So an airstone displaces CO2 by the physical bubbling movement, rather than by actual O2 dissolving ??

 

[russellbrooke]

I do like having an airstone in the tank. I think it looks quite nice.

 

[Themuleous]

So an airstone displaces CO2 by the physical bubbling movement, rather than by actual O2 dissolving ??

Yes, I would think so.

Guess you could run both at the same time, may just need to add more CO2 to compensate.

Sam