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  1. We are after as many aquarium plant images that we can get, doing so will assist us in completing the aquarium plant database.

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Switching to EI

Discussion in 'Journals' started by edelry.junior, Jan 2, 2017.

  1. edelry.junior

    edelry.junior Plant Enthusiast
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    Christophe I have been trying to learn more about the whole chemistry side of the hobby. You once explained to me the whole "1 point pH drop adds roughly 30 ppm" thing, and also that atmospheric CO2 (roughly 400ppm) levels cause our water to have around 3ppm of CO2, under NTP. I tried applying Henry's Law to calculate it but I am finding different values, something around 1.6ppm.


    I am sure I am doing something wrong, could you please help me? Are you familiar with the calculations?


    Tom Barr Do you have a bit of time to explain this Tom? Why do we consider 3 ppm as a start point?
     
    #101 edelry.junior, Feb 10, 2017
    Last edited by a moderator: Feb 10, 2017
  2. Christophe

    Christophe Subscriber
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    A very good question. When I posted that answer a few months ago, I actually did work though Henry's Law, and came to the same conclusion.


    I didn't want to dig into it at the time in answering, as I had always seen 3 ppm posted about as the normal atmospheric level for dissolved CO2, put up by people with more background than me.


    It remains that a pH drop of 1.0 or better seems to work well for many people. Just where this fits on the chart, and what the actual CO2 concentration should be might be up for discussion.


    I'll dig into this later when I have more time.
     
  3. fablau

    fablau rotalabutterfly.com
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    Beautiful tank Edelrly. How do you make the moss wall? What is the support for it?
     
  4. edelry.junior

    edelry.junior Plant Enthusiast
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    Hi Fablau, hope you are doing fine man :)


    it is just a "sandwich" of moss using some net, some stuff as in fish net. It is stretched on the wall, with suction cups sewed in. I crisscrossed and stitched it together to avoid it not being flat and instead becoming a bag. I hope it works, wir schauen mal ;)
     
  5. fablau

    fablau rotalabutterfly.com
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    Simple but clever! Thanks for the tip, some day I'll try that as well (now that finally my moss grows again!)


    As you said in German: Vedremo! (in Italian) :)
     
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  6. edelry.junior

    edelry.junior Plant Enthusiast
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    So, I have been really diving into this CO2 topic, to understand it from the science side. One thing that is still ringing in my head is the 1 point pH drop and the amount of CO2 present in water from atmospheric CO2. After checking and rechecking I must say that I feel confused.


    I played around with Henry's Law, mostly with the solubility being defined via concentration, so that I can finally find it. That can be calculated using [CO2(aq)] = KH x pCO2


    To calculate the CO2 partial pressure I considered that the air had 0,037% CO2 and temperature is 25C, and to be a bit precise, we discard the water vapour pressure by using this equation: pCO2 = (P° - pH2O) * XCO2


    The result is:


    pCO2 = (P° - pH2O) * XCO2


    pCO2 = (1,0000 atm - 0,0313 atm) * 3,7 x 10-4


    pCO2 = 3,69 x 10-4 atm


    I dont think removing the water vapour is relevant, but I did anyways.


    From there we proceed with the rest.


    [CO2(aq)] = KH * pCO2


    [CO2(aq)] = 3,38 x 10-2 * 3,69 x 10-4 mol x L-1 x atm-1 x atm


    [CO2(aq)] = 1,25 x 10-5 mol x L-1


    and then convert it to mg/l:


    [CO2(aq)] = 1,25 x 10-5 * 44 x 103 mg x L-1


    [CO2(aq)] = 0,55 mg x L-1


    So, in the end I am looking at this 0,55ppm value and wondering, is that it, really?


    A 1 point pH drop would add 5,5ppm. Considering that the water is not completely degassed from one day to the other, it would be possible to higher levels after a couple days.


    But still, wow, if this is right then man, CO2 without injection is low.


    Somebody with more experience would like to comment?
     
  7. Christophe

    Christophe Subscriber
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    I'd been looking into it as well, running through the same calculations and coming up with the same values.


    Something to keep in mind -- these calculations are for outdoor concentrations of CO2, currently 380-400ppm atmospheric depending on the source. Turns out that in our houses, we accumulate significantly higher levels, depending on how well ventilated and circulated the house is, how big, how many people. We add a CO2 cylinder that's bubbling out for much of the day into our homes also! It might not be uncommon for us to be running a home CO2 level of 1000-2000 ppm depending on various circumstances.


    See http://healthybuildingscience.com/20...o2-in-the-air/ for one such discussion.


    Reworking the calculations from different ambient CO2 levels leads to different degassed CO2 levels in the aquarium. How 3ppm as a baseline (associated with about 2000ppm ambient air CO2) got stuck in my head, I don't know.
     
  8. edelry.junior

    edelry.junior Plant Enthusiast
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    True.


    Thanks for adding more info into this discussion.


    I was also seeing this page: http://www.seafriends.org.nz/oceano/seawater.htm


    It refers to a 90ppm CO2 concentration in the oceans, which is interesting, because "as salinity increases, the amount of gas dissolved decreases because more water molecules are immobilised by the salt ion." Then it would mean that fresh water would hold much more CO2 at NTP. Im lost :(
     
  9. Christophe

    Christophe Subscriber
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    Despair not :)


    Like so many things in science, we can't truly nail down what's happening in our specific environments, because there are details we aren't taking into account. We might not even know what all to take into account.


    So so we lean on imperfect models to make rough estimates, which still might be way off.


    "Essentially, all models are wrong, but some are useful ".


    George E. P. Box


    Hopefully, we're at least biasing our systems in the right direction. Look at your tank. That's evidence that you are!
     
  10. edelry.junior

    edelry.junior Plant Enthusiast
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    You are right, just me being a drama queen.


    I guess the whole change into EI opened my eyes to all the knowledge laying around the hobby.


    I mean, I basically ate the Barr Reports I have.


    My goal is just to understand more behind CO2. The "ground" CO2 value in water, at NTP, was my starting point. Doesn't amount to much I guess :)


    If we use a 2000ppm CO2 concentration for our inddor environments, then the CO2 value in our tanks, without CO2 injection, would be around 2,75ppm. Thats interesting. It would also mean that a 1.5 pH drop would add a bit more than 80ppm. Thats a whooping amount.


    Maybe measuring the volume being injected (last time I measured it was a bit more than a liter per day, around 2g per day) would be better.


    2g of CO2 in 60l tank is roughly 33ppm. That is also interesting.


    But you are right, to get good results I do not need it. This is just for the knowledge, but not required for the practice.


    Thanks for the kind words Christophe :)
     
  11. edelry.junior

    edelry.junior Plant Enthusiast
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  12. edelry.junior

    edelry.junior Plant Enthusiast
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    Also a video...


    [video=youtube_share;nJd53u9tRUk]

     
  13. fablau

    fablau rotalabutterfly.com
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    Wow man, your plants perl like crazy! How much light do you have? Do you know your PAR? Maybe you already wrote that somewhere... It looks great though, very ealthy, keep it up!
     
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  14. Christophe

    Christophe Subscriber
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    Looks good & clean -- Keep it up!
     
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  15. edelry.junior

    edelry.junior Plant Enthusiast
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    Thanks a lot guys :)


    I am very thankful to you too, learned a lot here...


    Hands down the best forum when it comes to quality/experience of the members...


    I am playing with the lights Fablau, to see how fast I can go.


    I will not keep it like this, as it is a lot of work, but I want to test myself, and how stable I can keep things.


    Also, I wanted that moss wall done yesterday.... :)


    have 4x24 T5HO plus a 39w A601 Chihiros Led. Something around 7000, maybe 8000 lumens?
     
  16. fablau

    fablau rotalabutterfly.com
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    I see... well, I bet you have not less than 150 PAR at the substrate by looking at your pearling. Definitively high light, and I see you are handling them perfectly.


    Appreciated your kind words and glad to have helped you in some way! It's a pleasure to read your thread and your progress/experiments. Looking forward for the next update :)
     
  17. burr740

    burr740 Micros Spiller
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    Looking very nice!
     
  18. edelry.junior

    edelry.junior Plant Enthusiast
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    Thanks Burr, I owe a lot to you guys. The effort that you and Pikez put into your threads really open the way for noobs like me to have a chance.


    To think that in last December I was doing so poorly. I am really glad to have had the chance to learn as much as I did. And there is a lot more ahead.


    [​IMG]
     
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  19. fablau

    fablau rotalabutterfly.com
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    Impressive sequence, those pictures should be used in Tom's book about the Estimative Index (whenever he'll publish a book about it!)
     
  20. Tom Barr

    Tom Barr Founder
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    George Booth came up with that from years ago, it seems pretty close for most cases, recall that bacteria(mostly) and fish add some CO2 as well. Tannins and leaching from plants also affect the pH.


    A method to get a real accurate measure on it's baseline is to take sample water and use a pH probe with a O2 membrane and fill with a KH reference solution and then take the measure and adjust for the KH inside the pH probe's DO membrane. You can run a pH probe side by side to get the lag time associated with the pH measures between the two probes.


    This will give the pH off set, the lag time for the DO membrane CO2 reference pH probe and the true CO2 value.


    So that's a way to get the CO2 base line.


    But..............that's still a moving target in your tank, but at least you have a point to start from and can use the off set value to adjust the CO2 start and end relative points.


    There's a good 5-8 different methods to measure CO2. We use several typically, not just one. Even though most times we really do not think about it.
     
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