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More on CO2 issues

Discussion in 'Advanced Strategies and Fertilization' started by Tom Barr, Sep 28, 2005.

  1. Tom Barr

    Tom Barr Founder
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    Repost from the APD:

    Are you sure you want to know how organic acids influence pH?

    I'd suggest a method that side steps all that mucky stuff.
    If you are truly interested, there is a definitive book on the topic of the limnology of humic waters. Check the local College library system(or book vendors etc). Applying it to a planted tank will be a challenge (I've read the book when I was at UCSB).

    To side step pH influences and to get a rough estimation from very low even absent KH's:
    Measure the pH/KH in the tap water you use after it sits for 24 hours.
    Next, estimate the target for CO2 you want(say pH 6.5 and a KH of 4).

    You can add a stable amount of CO2 and _then_ add the tannins. As long as you are adding the CO2 in a stable manner(eg , no pH controllers!!!), the plant uptake of CO2 will be relatively similar.

    So if the pH is 6.5 without the tannis influence and is now 6.0, you have the fudge factor of 0.5 pH units for this amount of tannins. We do not measure tannins in our tanks, this is a variable and one we cannot get at easily(they do sell tannins test kits).
    Thuis is improtant to note that the tannins levels do not stay the same in our tank, many make this mistake in assuming so (thus a bad idea to use a pH controller in these situations).

    The CO2 being added for the plants is the SAME in both cases(ph 6.5 and the pH 6.0).
    We will assume that plant demand for CO2 is also the same as well as non limiting light/nutrients.

    KH can be addressed in a similar manner. By taking a CO2 measurement, as well as a gauge for plant health at a KH of say 4, you can maintain the the same CO2 dosing rate, then remove all the KH. KH = 0.

    You are not able to measure the CO2 but you are still adding the _same amount of CO2_ from the measurement at KH = 4, and the plant uptake will also be the same or very close(we will assume it is). The only variable is the KH that you are changing.
    So having KH is not needed even if you use this back door method.
    Plants care about CO2, not the KH *(it would seem).
    They do make ultra pure pH testing methods for very low alk waters.

    For our application, I think this is the easiest solution.
    If you suspect the tap water and other organic or inorganic issues influencing the KH, do this also very simple backdoor test:

    Take reading of the tap, see what the KH is. Next make a reference solution using pure DI water+ baking soda to get the same KH. Test this reference solution with the same test kit.

    Any difference?
    If so, then the difference is likely from the non bicarbonate alk.

    You should be able to make a ref solution for KH with about 1-2ppm of accuracy using a scale/teaspoon x 20 measurements with an accurate scale.
    Simply add the known volume of puire DI water in liters/grams.
    Then you can check those pesky KH test kits for accuracy.

    This is seldom ever done yet folks rely heavily on KH test ktis while spending $$$ for accurate pH measurements.

    Tannis and other acids change over time(and can be added to the tap water peroidically to perform various functions for the Utility company), stray current changes in many cases depending on the device being on, and few folks ever calibrate their KH test kits. These issues can cause problems for controller users if they are complacent and do not also eyeball the plants as their "test kit". I saw plenty of evidence for this recently with user error.

    Doing so may resolve many of the seemingly excess CO2 ppm levels that folks are seeing.
    Given that 95% of algae issues are CO2 related, you'd figure this is a good place to really focus on improvements in measurement, accuracy and methods for practical use.

    Regards,
    Tom Barr
    www.BarrReport.com
     
  2. defdac

    defdac Lifetime Members
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    Re: More on CO2 issues

    What do you think about the breathing-test where you blow down with a straw in a small cup of aquarium water in 5 minutes giving you apx 30 ppm CO2?

    No KH-tests needed. You'll recieve a pH-test-color to shoot for, not needing to know what pH the color actually means and wheater the pH-test is good or not either.
     
  3. brad

    brad Prolific Poster

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    Re: More on CO2 issues

    wouldn`t it be kinda hard to keep up with what`s being gased of and what`s being used by the plants? defdac, I have this image in my head of you passing out face first in your tank and drowning. :eek:
     
  4. fosteder

    fosteder Guru Class Expert

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    Re: More on CO2 issues

    I mean no offense in this post defdac...but I really fail to see how that sort of test can be accurate at all. Considering all of the factors (cup size, dispersion method, rate of exhaling...etc) I don't think you could come close to assuming it is near 30 ppm of CO2. I may be wrong, but you asked for opinions. ;)
     
  5. Tom Barr

    Tom Barr Founder
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    Re: More on CO2 issues

    I'm not clear on this.
    Paul K was enamored with breathing into a bag and using that as a CO2 supply.

    I'd rather stick with bubble rates out of a standard orifice(say 1/8" or the mm equilivalent)

    Assume the pH drop alone as a standard for CO2 dosing, I think this is what you are suggesting?

    Regards,
    Tom Barr
     
  6. defdac

    defdac Lifetime Members
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    Re: More on CO2 issues

    No no, not using my breath to get CO2 in the aquarium like Paul K:s funny experiment here http://www.thekrib.com/Plants/CO2/mouth.html :)

    No, what I meant was the Krause-thingy: If one blows down a small cup of aquarium water with a straw the water will after a couple of minutes reach some kind of equillibrium with the CO2-content in your breath - which happens to be around 30 ppm.

    So when you measure the pH in the little cup with your lousy pH-test it will give you a color to shoot for.

    A kind of ~30 ppm calibration, without the need of knowing what the KH is or how organic acids will influence the test.
     
  7. unirdna

    unirdna Junior Poster

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    Re: More on CO2 issues

    Ahh, I get it. But considering all the $$ we pour into the hobby, what's another $4 for a KH test kit? Still, that kind of quick-n-dirty test would be good to know if you were in a pinch. Maybe I'll try it out on Sunday if the Packers decide not to show up for the game (again).
     
  8. Tom Barr

    Tom Barr Founder
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    Re: More on CO2 issues

    If you assume the glass of water will always be 30ppm..............

    I'm not sure I'd go there.

    Regards,
    Tom Barr
     
  9. defdac

    defdac Lifetime Members
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    Re: More on CO2 issues

    It seems to be for everyone that does this test.

    But the point is that it have helped a lot of beginners thinking their expensive pH and KH-test kits shows them they are right on target but still have no pearling plants. Ofteb the breathing test gives them a much lower pH reading - and when they target this lower pH the pearling get better.

    Still, it's mostly for test-, math-, chart- and ppm-fanatics that have got stuck between tests and numbers with plants that doesn't pearl.
     
  10. Tom Wood

    Tom Wood Guru Class Expert

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    Re: More on CO2 issues

    My (unsoftened) tapwater KH is 14 degrees, the GH is 24 degrees, the TDS is 420ppm. I'm using RO water in my 90 gallon tank and reconstituting it with a few gallons of hard water. However, I'm also using some Discus Buffer (monosodium phosphate) as a PO4 source, so that's throwing off the CO2/pH/KH chart. But since I know how much PO4 is in the water, is there a way to readjust the chart?

    Edit: Also, is the KH test inaccurate with PO4 present, or is it just not reporting the correct amount of carbonate for use in the chart? That is, is it testing high and the water is really not buffered as well as the test suggests? Or, the KH is correct, but the amount of carbonate is somewhat lower?

    TW
     
  11. detlef

    detlef Subscriber

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    Re: More on CO2 issues

    Hi,

    I found from reading in my old Krause book that if you blow your breath into a cup of water with a straw you will end up having 60ppm of CO2.

    Regards,
    Detlef
     
  12. defdac

    defdac Lifetime Members
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