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A way of measuring CO2 concentration

Discussion in 'CO2 Enrichment' started by scottward, Sep 12, 2011.

  1. scottward

    scottward Guru Class Expert

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    Ok, we know that CO2 builds up at the top of our CO2 reactors; the size of the air gap getting larger later in the enrichment period.

    Just wondering if it is possible to somehow use this as a means of measuring CO2 concentration.

    Just thought I'd throw it out there.

    Is there any way of metering the CO2 that won't dissolve as a way of determining the CO2 concentration.

    This might be a little bit silly - but who knows.

    Probably too many variables to control??

    But if it were possible to control the variables somehow, would it not be possible to calculate how much CO2 is in solution by observing the size of an air gap against some kind of calibrated scale?

    Scott.
     
  2. grshs_vny

    grshs_vny Prolific Poster

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    Yes.

    Scott previous night installed my new reactor and thought the samething.First you have to measure gas build up in a known period of time and the rate of increase in build up with reactor off,then run the reactor for few minutes so that the CO2 mix up becomes steady.Now with reactor running measure the rate of increase in gas build up and correlating the tiny bubbles escaped from the reactor and the resistance exerted by the gas build up to the CO2 flow it is possible to measure to certain extent.It seems very easy but it's not.You have to consider every variables like turbulence,burping,etc.
     
  3. nipat

    nipat Guru Class Expert

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  4. Biollante

    Biollante Lifetime Charter Member
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    I Assumed Nipat Had Been Doing This All Along


    Hi,

    Nipat is of course, as always, right[SUP]1[/SUP],:) a good (cheap) way to calibrate your pH controllers or other devices for your water conditions is to put a known quantity of CO2 into your aquarium water.:gw



    1. [SUP]2[/SUP]Rinse a clean open mouth container in the aquarium water to be tested.
    2. Take a sample 1000-ml[SUP]3[/SUP] (500-ml and 220-ml samples are also easy to work with) from beneath the surface of the water.
    3. Place a coffee filter over the opening on the jar and let sit for at least 12 hours.
    4. After 12-24 hours open a fresh (as in not opened previously), room temperature soda water and pour 50-ml of soda water[SUP]4[/SUP] into an open container and wait 5-minutes
    5. Remove the coffee filter and test the pH of the aged aquarium water, about mid-depth, do yourself a favor and write this down
    6. Remove (pour off) enough aged aquarium water to leave 950-ml
    7. Now carefully pour the 50-ml of soda water into the aged aquarium water.
    8. Stir gently with glass stirring rod[SUP]5[/SUP]
    9. Measure the pH again from mid-depth.

    This process can be used to calibrate your controller, assuming you are using your controller to measure pH, simply start with 950-ml of water (remember evaporation).

    If you are at sea level on a standard day and the temperature in your “room,” is 25C, you have added about 30-ppm of carbon dioxide to your aged aquarium water and for most you will measure approximately 1-degree drop in pH.


    • The higher your density-altitude and temperature the less CO2 will be in solution.


    • Higher pH, higher carbonate hardness (KH) will tend to somewhat reduce the difference between beginning and ending pH levels.


    • A lot of organic material, biological activity in the water column can over state (that is increase the) difference in pH levels.


    Purists may wish to aerate the sample during the 12-24 hour period.

    Biollante
    [SUP]1[/SUP]Ihave a macro for “Nipat is of course, as always, right.”
    [SUP]2[/SUP] Nothing in this post should be considered scientific or anything but the incoherent ramblings of a ridiculous old potted-plant. I try to be reasonably sure that it is factual that it does not conflict with what recognized experts understand. At the same time this is not a scientific paper, it is one hobbyist speaking to other hobbyists.
    [SUP]3[/SUP]Measuring by weight rather than volume provides greater accuracy.
    [SUP]4[/SUP] At 1 atmosphere (101.3 kPa) and 25C
    [SUP]5[/SUP]Doesn’t actually have to be glass, mainly not bugger digging digit, clean stainless steel spoon or knife, clean plastic straw, emphasis here is on “clean and non-reactive.”
     
  5. scottward

    scottward Guru Class Expert

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    Thanks - but what does this have to do with my original question "would it not be possible to calculate how much CO2 is in solution by observing the size of an air gap against some kind of calibrated scale?" :)
     
  6. pat w

    pat w Member

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    Not that I enjoy being a buzzkill but can you be sure that the bubble is exclusively CO2? It might have some out gassed nitrogen or oxygen that would throw off the calculation. After all, there's the production of O2 by the plants and there is allways the possibility of de-nitrifing anarobic prcesses going on deep in the substrate.

    Pat
     
  7. Biollante

    Biollante Lifetime Charter Member
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    Mfc


    Hi Scott,

    For a variety of reasons including Pat’s, I believe the answer is no the pressure build can do more than give a very rough idea at best. :)



    It is interesting in a couple of my do-it-yourself CO2 tanks the pressure in the “reactor” can vary from something like 5-12 inches (1.2-3 kPa) and yet maintain reasonably stable CO2 delivery.:confused: In this case the main factor seems to be temperature

    Even using rotameters the problem of fluctuation exists
    :rolleyes:, the only sure device I have seen are mass flow controllers and frankly only a complete moron would spend that kind of money to measure the flow of CO2 into an aquarium.:eek:

    Biollante



     
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