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Question about co2 overdosing

Discussion in 'CO2 Enrichment' started by dazzer1975, Apr 17, 2007.

  1. dazzer1975

    dazzer1975 Prolific Poster

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    First off, let me say, I simply want to understand a few things here, hence I am asking the question, I do not want a flame war.

    Working on the "assumption" (I highlight assumption as I do not know what I am about to say as fact, therefore want people opinions as to how correct I am in thinking this) that fish deal with gasses through their gills via osmosis, and that I am working under the assumption that for a fish to rid themselves of co2 the surrounding water has to be of a lower concentration of co2 that their body is at, and this can continue up to a level of co2 concentration which varies for different types and sizes of fish (as evidenced when overdosed co2 previously with angel fish and ancistrus responding extremely badly and neon tetras and platties not seemingly bothered by these levels).

    Secondly, would I be right in assuming that agitating the surface of the water increases the rate of co2 drive off from the water column, while also increasing o2 levels?

    To kind of draw those two paragraphs together, I have the impression that it is not how much o2 is available to the fish as to whether they can cope with the increase in co2 levels, it is the amount of co2 in the water and in their bodies which determines whether the fish can expel this co2 and thus whether the fish suffer from a lack of oxygen. (Same principle with asthma, the biggest problem is exhaling, as opposed to inhaling which causes the sufferer to experience loss of breath) if the water gets so saturated with co2 that the concentrations are too high for the fish to expel their co2 into the water then the problems start, and it is not a result of low 02?

    Bearing in mind, its late (or early depending on your viewpoint) and I have been up all night and my way of explaining myself leaves a lot to be desired, would it be a correct conclusion to suppose that surface agitation of water, simply to enable you to throw more co2 into the water is a bit of a red herring which serves no other purpose than to use more co2 as neccessary (remembering surface agitation draws co2 out of water)

    Isn't it better to simply stock with lifestock at the accepted levels taking into account surface area of tank allowing for o2 exchange ensuring their oxygen requirements are met and then just using whatever co2 diffusal method you prefer to achieve the co2 concentration your lifestock seem comfortable with.

    Adding further o2 is not needed and nor does it allow higher concentrations of co2 owing to the way a fish deals with gasses?

    What do people here think?
     
  2. laka

    laka Prolific Poster

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    Dazzer
    As far as i can see your assumptions are correct. If you are concerned about your fish and for whatever reason you are not comfortable with CO2 levels of 30ppm in your water an easy solution is to set up a low tec non-CO2 tank.
    A high tec tank that is pearling with lights on has supersaturated O2. You could not pumps this much O2 in a tank with air stones alone. If fish were experiencing shortness of breath in such a case in the abscence of surface agitation then you could correctly assume it is CO2 poisoning (hypercapnia). I think surface agitation does facilitate in driving off excess CO2 that is not utilised by photosynthesis and at the same time introduces O2 into water.
    You would have to look at a physiology text to see what the affinity of CO2/O2 to the Hb molecule is. I cannot remember the biochemistry but there is a definite relationship.
    LAKA
     
  3. Frolicsome_Flora

    Frolicsome_Flora Guru Class Expert

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    creating more surface agitation does offgas co2 from the water column, but not by very much. Surface agitation also does increase the O2 levels in the water considerably, allowing the fish to cope with much higher levels of co2, (in my tank almost double). So long as your not adding co2 at night, and you have a good ripple on the water surface, your problems are going to be minimal provided your dialing in the co2 amounts with your drop checker properly.

    Id suggest that if your still having troubles and doing both of those things, that your co2 is way higher than you think it is... and therefore, excessive.
     
  4. dazzer1975

    dazzer1975 Prolific Poster

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    Ah this is at the very heart of what I am asking, but with my tired mind and poor explanation I failed to reduce it down to this cogent sentence I have quoted above.

    The assumptions I am working under is that it is irrelevant to the fish how much o2 is in the water (providing the surface area/stocking rule has been applied there will be sufficient o2 in the water for the fish) as increasing o2 makes no difference to the fish, how it deals with co2, as the problem with suffocation of the fish, is not one of low o2, but of high co2 which prevents the fish removing co2 in its body via osmosis into the surrounding water.

    Thats essentially what I am asking, because if that assumption is correct, then seeing as increasing surface agitation does nothing for the fish and it also helps to drive off the co2, then isn't it more efficient to simply not agitate the surface of the water thus attaining the desirable co2 levels while at the same time using less co2?

    As for whether my own set up is either too high in co2 and the problems I am having etc. I am having no problems, and haven't with this and fish health since the first week after using pressurised co2 a good year ago now.

    However, these are still questions I think would be interesting to know the answer to and to have a discussion about as I want to know whether my assumptions hold true or not, if they do, great, lets move forward and explore this, if my assumptions are incorrect, great, I can move forward and put that out of my mind.
     
  5. Frolicsome_Flora

    Frolicsome_Flora Guru Class Expert

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    you have it the wrong way around.. the main cause of suffocation is caused by lack of O2, not CO2 in excess. Although obviously massive levels of co2 are also going to cause an issue
     
  6. dazzer1975

    dazzer1975 Prolific Poster

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    So does that mean o2 becomes defficient as a result of co2 injection?


    If so, please could you explain how this happens, is it because as co2 diffuses into the water, it displaces o2?

    (sorry for non technical terminology, I am sooooooo no a scientist type chap lol)
     
  7. Frolicsome_Flora

    Frolicsome_Flora Guru Class Expert

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    No and no, CO2 does not replace O2, it mearly super-saturates, which is why when you provide surface aggitation some CO2 is lost.

    There is also another school of thought, by having increased CO2, with a good plant biomass and healthy growth, you will actually achieve a level of O2 in the water that is greater than normal because of the accelerated photosynthesis.. so one could argue, that by adding more CO2, your actually adding to the amounts of O2 held in solution regardless of surface aggitation. My own tests have shown though that no surface aggitation will result in very unhappy fish, very quickly.
     
  8. dazzer1975

    dazzer1975 Prolific Poster

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    CO2 Poisoning

    This post deals with what I am meaning regarding the gas exchange of co2 from the fish into the surrounding water and mentions that the fish should be able to cope at non excessive levels of co2 (which we can all testify to) and even, to a degree, increase its respiration to increase its o2 intake accordingly, thus I think I have finally grasped the idea of surface agitation while injecting co2.

    However, I do still have a niggle that sufficient co2 levels can be achieved without surface agitation thus ensuring fish dont over respirate (is that even a term lmao) and we dont use more co2 than is neccessary?

    I mean I am also using the assumption that 30ppm of co2 is quite adequate for planted tanks, if so, I know this can be acheived with quite a high stocking density of lifstock with no detriment to them and without surface agitation, or is 30ppm of co2 seen as more of a minimum target? I know it is all balanced with light levels, fish stock, plant biomass etc, but still, what do you think Flora?
     
  9. dazzer1975

    dazzer1975 Prolific Poster

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    You posted as I did.

    That makes sense, re accelerated photosynthesis increases o2.

    I have run co2 levels of 30ppm (all I have ever aimed for as I believed that to be the holy grail lmao seems I am about to be proven wrong again?) and never agitated the surface of the water and had no problems with fish behaviour at all, of course their respiration may have increased but there was no behavioural change that I could notice to signify this?

    Of course with co2 concentrations beyond 30ppm this will obviously be a different story
     
  10. VaughnH

    VaughnH Lifetime Charter Member
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    I think the belief that pearling indicates O2 saturation of the water is incorrect. Pearling only indicates that at the leaf surface, there are places where more O2 is released than can quickly be dissolved into the water, so a gas bubble forms. O2 doesn't dissolve easily into water compared to how easily CO2 dissolves, so the way water and O2 react is different from how water and CO2 react.

    Also, we never ever come anywhere near to saturation of the water with CO2. Water can dissolve in the neighborhood of 1000 ppm of CO2 - seltzer water, for example. Long before our tanks would reach that level even the plants would be suffering.

    I'm not a biologist by any stretch of imagination. But, I think excessive CO2 primarily bothers fish because they can't get rid of the CO2 in their blood, just as it does humans. I don't understand how it affects their ability to use O2, otherwise. I think Tom has explained this before, and as I recall I am incorect about the reason high CO2 levels bother fish - but being wrong occasionally never has bothered me too much!
     
  11. dazzer1975

    dazzer1975 Prolific Poster

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    Superb Vaughn, thank you for your input, very much appreciated.

    I have downloaded all prvious barr reports (again, reformatt hdd etc etc) except feb 2007 and will see if there is any further illumination in there.

    Again,

    thanks for the input.
     
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