CO2 and O2 - The Planted Tank Forum
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post #1 of 70 (permalink) Old 07-01-2011, 01:27 AM Thread Starter
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CO2 and O2

What is it specifically that can kill fish while dosing CO2? Is it the absolute concentration of CO2 or is it the relative concentration to O2?

Would running O2 through a reactor allow me to increase the CO2 levels?


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post #2 of 70 (permalink) Old 07-01-2011, 01:38 AM
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Excessive concentration of CO2 in water prevents the gills from transferring CO2 from internal to water.

Hemoglobin then can't absorb O2 from water.

Suffocation then results regardless of O2 availability.

Jim


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post #3 of 70 (permalink) Old 07-01-2011, 01:45 AM
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O2 and CO2 are separate. Amounts of one does not affect the other. In other words, more O2 doesn't push out CO2.

Running O2 probably creates bubbles though that "pop" at the surface....making it more difficult to keep CO2 in the water.

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post #4 of 70 (permalink) Old 07-01-2011, 02:09 AM Thread Starter
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so what is the limit for CO2 concentration?

30 ppm is desired but I have read that some people have run upwards of 40-50 ppm?


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post #5 of 70 (permalink) Old 07-01-2011, 02:25 AM
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it is relative, meaning that higher O2 levels will allow fish to tolerate more CO2
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post #6 of 70 (permalink) Old 07-01-2011, 02:27 AM
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Well, in theory, 40-50ppm CO2 is somewhere around the limit for many types of fauna ...but it doesn't really matter for our purposes. Unless you have some very expensive test equipment, you don't know what your concentration actually is.

Your best bet is to get a drop checker with 4dKH and pH indicator solution, up your CO2 until you get greenish-yellow by the end of the lighting period (which might mean you have somewhere between 20 and 40ppm - maybe), and then daily tweak the CO2 up just a tiny bit more until your fish or inverts start stressing out. Then dial it back a notch, and you have your limit.

Or, just aim for "Mountain Dew", assume it's good enough, and move on Oh, and either way, increased surface agitation, while allowing dissolved CO2 to gas out faster, will also insure that you've got enough dissolved O2 in the column. So, when your fish start to show signs of stress, at least you know it's not an O2 issue.
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post #7 of 70 (permalink) Old 07-01-2011, 02:33 AM Thread Starter
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Quote:
Originally Posted by VeeSe View Post
it is relative, meaning that higher O2 levels will allow fish to tolerate more CO2
but that is the opposite of what the previous posters just wrote

And essentially what my initial question was asking...

CO2 inhibits the uptake of O2 through the gills because hemoglobin prefers CO2 to O2, but.... if you increase the O2 concentration, will the greater difference in conc. between the water and the fish's blood help with binding of oxygen thus increasing the lethal concentration of CO2?

Kevmo:

I currently don't have any fish in the tank as I wanted to run some tests on the rates of plant growth. When I did have fishies, my DC was more on the yellow side with the 4dkh solution. I would start it about an hour before lights on and it would be at my chosen conc about an hour into my photoperiod. I agree about the usefullness of the DC's and it is really just an estimate with a lot of variables.

I was AND still am diffusing it through a cerges style reactor, so I do not have CO2 bubbles in my tank. I have read that misting is more efficient for co2 uptake in plants therefore you would not need as high of a co2 conc...is this correct?

EDIT:

With the fish gone, i have been blasting CO2, and the DC is basically pee yellow 24/7 and I gotta say I am getting wonderful growth Clearly fish would not last very long in this scenario so i was wondering if increasing the Oxygen would allow me to theoretically run higher CO2 concentrations without gassing any fish.


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post #8 of 70 (permalink) Old 07-01-2011, 03:16 AM
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I don't think I'm contradicting what they were saying. BlueJack said that adding CO2 doesn't push out O2, not that increasing O2 levels wouldn't help your fish tolerate more CO2. However, I don't think you can take this to "pee yellow" extremes even if you agitate your water surface well to oxygenate your water. Hope that helps!
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post #9 of 70 (permalink) Old 07-01-2011, 03:23 AM
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Quote:
Originally Posted by Jim Miller View Post
Hemoglobin then can't absorb O2 from water.

Suffocation then results regardless of O2 availability.

Jim
^ That

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post #10 of 70 (permalink) Old 07-01-2011, 03:45 AM
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TEST KIT http://www.fondriest.com/products/hach_143601.htm (200 tests 35 bux)

also mr barr may butt in but c02 can easily be 5-10 times the concentration of o2 and be totally safe, c02 exchanges 20 times easier than o2,(that's how respiration works, c02 has to be exchanged in order for o2 to be absorbed) if there isnt more c02 in the water column than o2, guess what, respiration becomes difficult.. Fish work much the same as we do just underwater. the lethal dose of c02 to a human is 100,000 ppm or 10% of total air, the suggested dose is 1500ppm and current air quantity is LOWER than the suggested dose, currently at 380ppm avg. the lethal dose is 263 times what current levels are. more o2 can mean more c02 relatively. getting it there however is inefficient, thus the general 30ppm rule of thumb. every plant is different to a degree and so are fauna. my tank hovers at 45ppm and everyone has beautiful coloration, just had swordtail fry the other day, good eating habbits, no disease..

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post #11 of 70 (permalink) Old 07-01-2011, 04:02 AM Thread Starter
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Quote:
Originally Posted by HD Blazingwolf View Post
TEST KIT http://www.fondriest.com/products/hach_143601.htm (200 tests 35 bux)

also mr barr may butt in but c02 can easily be 5-10 times the concentration of o2 and be totally safe, c02 exchanges 20 times easier than o2,(that's how respiration works, c02 has to be exchanged in order for o2 to be absorbed) if there isnt more c02 in the water column than o2, guess what, respiration becomes difficult.. Fish work much the same as we do just underwater. the lethal dose of c02 to a human is 100,000 ppm or 10% of total air, the suggested dose is 1500ppm and current air quantity is LOWER than the suggested dose, currently at 380ppm avg. the lethal dose is 263 times what current levels are. more o2 can mean more c02 relatively. getting it there however is inefficient, thus the general 30ppm rule of thumb. every plant is different to a degree and so are fauna. my tank hovers at 45ppm and everyone has beautiful coloration, just had swordtail fry the other day, good eating habbits, no disease..
So you are saying that you CAN increase O2 to increase the tolerable levels of CO2?

In order to maintian your 45 ppm, how are you diffusing CO2? Do you have any surface agitation/O2 addition to help?

EDIT: Also would decreasing the temperature of the water result in greater possible CO2 concentration since the O2 saturation will increase? A tank temp of 70F vs 80F corresponds to an O2 saturation of ~ 8 and 9 respectively, therefore assuming that 5x the CO2 concentration is acceptable, that leads to CO2 ppm of 45 instead of 40...


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post #12 of 70 (permalink) Old 07-01-2011, 04:16 AM
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yes, however trying to introduce more c02 and more o2 leads to wasted materials, you can safely grow almost anny plant at 30pppm of c02. that being said, i have a fine pore bubble stone and and koralia 425gph pointed slightly up for agitation, plus a 1/2 inch drop from my spray bar at 210gph measured. c02 diffusion is done by a cerge reactor.

note if ur plants arent using the extra c02 its pointless

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post #13 of 70 (permalink) Old 07-01-2011, 04:21 AM Thread Starter
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hmmm...so 30 ppm should work regardless of light intensity? I figured if you are under very high light (lets say 4 x t5ho bulbs) 30 ppm of CO2 would not be enough to balance that.


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post #14 of 70 (permalink) Old 07-01-2011, 04:36 AM
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You could just take out some of the bulbs. You can pretty much grow anything even if you remove half the bulbs.
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post #15 of 70 (permalink) Old 07-01-2011, 04:42 AM Thread Starter
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I know...I can also raise the fixture and reduce the photoperiod but I am curious about this from an academic standpoint.

Is it possible to be CO2 limited at 30 ppm?


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