CO2 and O2 levels

[scottward]

Just trying to check my understand of CO2 and O2 levels in the tank, with respect to fish...

Is it correct that CO2 enrichment DOES NOT displace O2? i.e. if there is an O2 level of Xppm in the water and you start raising the CO2 leve (by reactor, needlewheel, whatever), irrespective of how high you push the CO2 level, the O2 level will remain at Xppm (discounting any consumption by fish/bacteria)?

Does CO2 have any direct toxicity to fish? Or is it really an indirect affect upon the fish in that it affects the fishes ability to uptake O2?

I assume that the effect of CO2 upon a fishes ability to uptake O2 kicks in at low levels of CO2? So, even at say 10ppm of CO2, the ability for a fish to uptake O2 will be hindered somewhat? The fish won't usually gasp though at 10ppm of CO2 unless there is a chronic shortage of O2?

Ok - so, a fish could be fine at 50ppm of CO2 *provided* there is ample O2 in the water? The fishes ability to uptake the O2 is being affected by the CO2 *but* because there is ample O2 in the water the problem is mitigated?

Hence the reason why some surface agitation is important; some CO2 gas will be wasted requiring us to ramp up the CO2 enrichment mechanism but, the surface agitation will increase the O2 levels hence mitigating any inhibitation the fish might have to using the O2 at higher CO2 levels?

Do I finally have my head around all this?

P.S. Tom, you pump O2 into your tanks sometimes? Is this so that you can keep the water surface dead still to minimize CO2 loss? Is there any other ways of boosting the O2 in the water other than surface agitation/O2 injection?

P.P.S. Yeah I know, I know, too many questions in one thread. If you stand a glass of tapwater for, say, 24 hours, I understand that the CO2 level will be about 2-3ppm (equalising with the .0003% in the air). Because oxygen is about 21% in the air, does this mean that the glass of water will, once it reaches equilibrium with the air, have several thousand ppm of O2? I'm guessing not, due to differences in partial pressure etc?

 

[shoggoth43]

Based on what I've read, I think it's more a case of with the higher CO2 concentrations the fish have less ability to get rid of the CO2 in their blood, and thus they can't replace it with O2. It's semantics, but with most of the submarine and space articles I've read, you can pump O2 into the chamber all day, but if you don't scrub the CO2 out, you still end up with dead astronauts/submariners since they can't get rid of the CO2 in their blood.

"Does CO2 have any direct toxicity to fish? Or is it really an indirect affect upon the fish in that it affects the fishes ability to uptake O2?

I assume that the effect of CO2 upon a fishes ability to uptake O2 kicks in at low levels of CO2? So, even at say 10ppm of CO2, the ability for a fish to uptake O2 will be hindered somewhat? The fish won't usually gasp though at 10ppm of CO2 unless there is a chronic shortage of O2?"

 

[scottward]

That's interesting about the CO2 stuff on submarines etc, I didn't know about that. Although I have watched, and love, the movie Apollo 13... ;-)

I understand that O2 diffuses into the bloodstream of a fish at the gills, and CO2 diffuses out same location? This is because the O2 level in the blood is lower than the surrounding water, whereas the CO2 concentration in the blood is higher than the surrounding water...correct?

So, unless the CO2 levels in the water are incredibly high, I can't see this being an issue...

At lower CO2 levels, as per my previous question, is there some other mechanism that is hindering O2 uptake?

 

[scottward]

CO2 can reduce the oxygen affinity of hemoglobin

Ah...now I might be getting somewhere? Found this doing a 'Google' search.

Hmmm.

 

[shoggoth43]

Basically too much CO2 concentration means the hemoglobin doesn't "let go" of the CO2 and grab the O2 since it likes CO2 more. This is the same problem with carbon monoxide as well.

-
S

Ah...now I might be getting somewhere? Found this doing a 'Google' search.

Hmmm.

 

[scottward]

Ok, so by upping the O2 levels, your "coercing" the hemoglobin to take on more O2?

 

[shoggoth43]

Within limits. You can have 89% O2 and 11% CO2 ( rough guess numbers from what I remember, don't take them literally as I'm just trying to illustrate a point ) and still have a problem if the affinity for CO2 isn't overcome. The only way to get it to let go is to give it a reason, i.e. lower concentration of CO2 in the atmosphere/water. Whereas you might have 80% O2, and 6% CO2 and be fine. In most cases, at least for people-in-pressurized-cans, you don't usually worry too much about O2 so much as you do getting rid of CO2. I'm assuming this is much the same process for fish, but I could be way off base here.

-
S

Ok, so by upping the O2 levels, your "coercing" the hemoglobin to take on more O2?

 

[rogerjackkson]

As far as I know, spread to the blood oxygen and carbon dioxide diffuses out of the gills the same location? This is because the oxygen concentration in the blood is lower than the surrounding water, and carbon dioxide concentrations in the blood than the surrounding water.

 

[barbarossa4122]

Interesting thread/subject. Now, I am wondering if I, should run my air stones only when the co2 is off or 24/7.

 

[Cyclesafe]

I was surprised to find that to maintain CO2 with my 920-gph-at-zero-head-internal-pump-fed under gravel jets and spray bar operating that I only had to increase CO2 flow by 1/2 a notch on my Ideal Valve vernier knob. I now have it on 24/7. The tank is crystal clear and there is no mulm or detritus. I think an air stone will have a minimal detrimental effect on CO2 concentration. It's certainly worth it to see for yourself in your tank....

 

[barbarossa4122]

I did run air stones 24/7 without increasing co2 and did not like the results. For now, running air stones when co2 is off seem to work for plants and creatures. But, I am willing to experiment again by running air stone 24/7 and increase co2.

 

[ShadowMac]

something, I have observed is how the CO2 is injected with regards to if an airstone is needed. I first used an inline reactor which dissolved CO2 before adding it into the aquarium. This method was not ideal as I had difficulty reaching good CO2 levels and my fish reacted negatively to this much dissolved CO2, so I began to run an airstone which improved things greatly. It increased O2 and probably degassed small amounts of CO2 as well. I had always had one or even two koralia pumps rippling the surface, but that never seemed to be enough.

I have since completely removed the inline reactor and have been using a glass diffuser while I wait for my new regulator and inline atomizer (my current reg setup couldn't handle the working pressure of the atomizer) and now do not need to use my airstone 24/7. I run it at night only now. Much of the CO2 is in the form of small bubbles instead of completely dissolved. Plants have been responding even better to this after 2 weeks. I can't wait to see what the atomizer does.

In my 20 gallon I have been running an inline atomizer with nearly glass like surface and an airstone at night with great results. Shrimp haven't shown much for signs of CO2 stress, although I'm still worried about a end of tank dump that could wipe out my nice shrimp, so I will probably be moving them to a 10 gallon low tech for a breeding colony.

it is dissolved CO2 only that inhibits a fish's ability to respirate due to concentration gradients, diffusion and the interaction of CO2 on hemoglobins affinity for oxygen, ph drops in the blood due to dissolved CO2 decreases hemoglobin's affinity for O2 causing it to release O2, alter its shape and pick up CO2 for transport out of the gills, so I would assume that high levels of dissolved CO2 in the water would act in a similiar way, decreasing hemoglobin's O2 affinity by preventing structural changes in the protien from occuring that release CO2 and cause hemoglobin affinity to be greater for O2 than CO2.

So if we provide our CO2 in two forms, dissolved and misting all of it is available for plants, and less is impacting respiration in fish. This makes a strong case against reactors that completely dissolve CO2 before injecting it into the tank. A lesson I learned through struggles that can now be attributed to my reactor, which is for sale if someone wants it!

 

[Matt F.]

I find that my fauna can handle higher levels of co2 in my tank w/o issue as long as my flow ripples the surface and the fish are used to the level.The flow from the filter doesn't have to be too intense...just enough to ripple the surface.

Figure, I am at a yellow color in my drop checker after 5 hours of injection. I use 4dkh (over 30 ppm). I think we have to look at the gas levels in a fishtank as a system with many parts. There is current, artificially injected air, and photosynthesis increasing O2. respiration, decomposition, and co2 injection increasing CO2 levels all at one time. These gasses are being metabolized at a certain rate. This rate, I would assume is variable.

Could be wrong, but...

 

[barbarossa4122]

Figure, I am at a yellow color in my drop checker after 5 hours of injection. I use 4dkh (over 30 ppm).

I am getting to yellow in 4h and 45min (yes, I timed it). My co2 starts 2hrs before lights on and stops 2hrs before lights off. Air stones start with lights and co2 off. Fish, shrimps and plants are doing great.

 

[scottward]

I am getting to yellow in 4h and 45min (yes, I timed it). My co2 starts 2hrs before lights on and stops 2hrs before lights off. Air stones start with lights and co2 off. Fish, shrimps and plants are doing great.

This intrigues me. My understanding is that plants ramp up there CO2 usage within abour 1 hour of lights on. If your system is taking 5 hours (excluding drop checking delayed response) to get the CO2 up, doesn't this suggest that the CO2 levels must be very low earlier in the photo period?

If this is the case, I'm confused as to how your plants can be doing great?

But well done all the same if they are doing great.

Scott.

 

[barbarossa4122]

This intrigues me. My understanding is that plants ramp up there CO2 usage within abour 1 hour of lights on. If your system is taking 5 hours (excluding drop checking delayed response) to get the CO2 up, doesn't this suggest that the CO2 levels must be very low earlier in the photo period?

If this is the case, I'm confused as to how your plants can be doing great?

But well done all the same if they are doing great.

Scott.

My co2 starts at 4 am and the lights at 6 am. This means that by 7 am or 8 am the latest my DCs are yellow. I excluded 2 hrs for the DCs delayed response. How can one get the optimal co2 levels by the time the lights come on if the co2 is off during the night ? My response to this was to start the co2 2 hrs before lights. Any other/better suggestions ?
My wife is trimming and pruning the plants once a week b/c most of them get out of control.

 

[barbarossa4122]

If your system is taking 5 hours (excluding drop checking delayed response)

It takes 5 hrs including not excluding the delayed response Scott If the DC is yellow at 9 am and you take out say, 2 hrs delayed response, this means the co2 levels were good at 7 am. Correct ?

 

[dutchy]

I think it's hard to make assumptions about the "right" Co2 level with something as crude as a dropchecker. How high is that "right" CO2 level? Can you name a figure, is it high enough for your tank and also putting the delayed response time at 2 hours is another assumption.

Not much to go on really. It just shows there is some level of CO2 in your tank after some time.

regards,
dutchy

 

[barbarossa4122]

Then, how do we know how much co2 is in our tanks. What is to guide us in obtaining good/optimal co2 levels ? DCs, pH, bubble counts ?
Btw, what is the delayed response for the DCs, in general ? 1 hr , 2 hrs.....?

Is anyone there that gets to lime green in an hr ? I can't and I am afraid to up the co2 b/c of the creatures.
Right now I use GLA atomic diffusers which work very well. I think 3 bps should be enough for a 55g tank (2 bps for the 30g and 0.7 bps for the 10g).

 

[dutchy]

Knowing how much CO2 is in your tank is one of the big problems. CO2 can vary multiple times in one hour. Your drop checker will never show that. I've also seen people gas their fish and still have CO2 deficiency signs because there's no circulation. pH/KH measurements are fairly inaccurate, being 0.1 pH off is 10 ppms of CO2.

I don't care about drop checkers, pH/KH values or bubble counts when it comes to CO2. Sure, I use a drop checker, but just to see in a glance that CO2 is still functioning. A deviation in colour makes me move into action. Also, a drop checker's colour is influenced by the accuracy of the fluid and how much light shines on the drop checker. More light is a lighter colour, just like holding any transparent fluid against the light. Not much to base the CO2 level on.

Let's assume your CO2 system is too small for the tank you have. One hour after lights switch on, CO2 demand could get so high that there's a temporary deficiency. Will the drop checker show it? No way. You will have algae but ask yourself how it's possible because the drop checker tells you everything is ok.

So what do I do? I use my plants and fish. I keep increasing CO2 until I notice the limits. These are no increase in plant leaf size or leaf diameter, or fish that show distress. One of both will show up first. That's the limit. Both are easy to notice. But I give it time. Not days, but weeks. That works both ways. if I notice leaf size or diameter decreases, I already know there's a problem with CO2.

The other issue is building a system that has enough capacity. I set myself a standard of being able to reach the desired CO2 level within the hour. That also ensures there's no lag in the system. Based on my previous mentioned limits.

With non controlled CO2 systems it's a bit harder. Driving up CO2 levels fast will create a problem later during the day. I prefer pH controlled systems. Sure, they're not perfect, and I don't care if the display says the pH is value XX. But it makes it possible to add lots of CO2 in the morning and keep it stable during the rest of the day.

regards,
dutchy