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Thread: Another way to determine CO2 in our tanks

  1. #1
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    Another way to determine CO2 in our tanks

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    I found this on TheKrib at http://www.thekrib.com/Plants/CO2/co2-meter.html.

    An extract:
    Krause describes a method in his book on aquarium water that is supposed to
    work with any kind of water. Not absolute pH is the key, but the change of
    pH by two units is used to determine correct CO2 concentration.

    Take a sample of your water and aerate it for some time until all CO2 is
    removed. In that case the concentration of CO2 is in equilibrium with
    the surrounding air (0.6ppm). Measure pH of the water (=X).

    Next exhale through a pipe into the water sample. After a while the
    concentration of CO2 in the water will assume 60ppm. Measure pH of the water (=Y).

    The optimum CO2 concentration of 10-20ppm is at the pH value about 2/3 of
    the difference between X and Y: pH,opt = X +.67*(Y-X).

    This will work even with buffered water, although the change in pH might be
    small and only detectable with an electronic pH meter.
    The book mentioned is a German book called "Handbuch Aquarienwasser" (Handbook of Aquarium Water) by Hans-J. Krause, ISBN 3-927 997-00-5.

    Any chem engineers/chemists, other people with relevant knowledge got comments?

    I'm wondering how long we have to breathe into the water before it hits 60ppm CO2.

    What if we want to determine the pH for 30ppm? Should be the pH halfway between X and Y?

    Can any German-reading member who travels to Germany often find the book and read up the details when he/she is there?
    Vincent - AQ is for everyone, but not for 'u' and 'mi'.
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    Can we inject CO2 from CO2 tank ? What happen we overshot and how to tell when we reach 60ppm ?

    Cheers

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    The idea is that our breathe has just enough CO2 in it that the water will equalise at 60ppm of CO2 eventually. Question is how long before that happens?

    Using CO2 from the tank won't work because we don't know at what level it will equalise.
    Vincent - AQ is for everyone, but not for 'u' and 'mi'.
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    I suppose with "pure" CO2 from our cylinders, the water will be saturated with CO2. But saturation point is different for waters with different properties like temperature... so unless we know these data, we don't know the ppm and hence can't project our desired pH.

    Our breathe will achieve a max at about 60ppm no matter what the water properties are as the concentration of CO2 in our breathe during normal breathing is more or less fixed.
    Vincent - AQ is for everyone, but not for 'u' and 'mi'.
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    I doubt this is a accurate method. CO2 in human breath can vary. Body at rest or at work can change the CO2 exhalation. I think you might get a more repeatable result using the CO2 from the cylinder. The only problem is that you do not know the purity of the CO2 in the cylinder.

    BC

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    Actually, what I'm interested in is the ambient ppm of CO2 in still water. Can't seem to find anything on the web regarding that. The extract says 0.6ppm. Is that correct? If it is then all we need to do is aim for a target of 1.7 to 1.8 pH lower then the pH of our tank water at ambient CO2.
    Last edited by vinz; 9th Sep 2005 at 15:37. Reason: Corrected pH drop value
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    According to my calculations, it is around 0.5ppm.

    BC

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    0.5, 0.6... close enough. A drop of 1.7 pH will give us between 30 to 40 ppm of CO2.
    Last edited by vinz; 7th Sep 2005 at 18:08. Reason: Corrected pH drop value.
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    Argh... made a mistake. Should look for a drop of about 1.7pH. Will edit above post...
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    To get a pH reading at ambient CO2 in your water, take a sample of your tank water in a clean container. Shake or stir the sample vigourously for a few minutes to release excess CO2. Then let the sample sit for a day, or better yet aerate the sample for a few hours. Measure and note the pH. The target pH you should be aiming for in your tank should be at least 1.7pH lower then this measurement.
    Vincent - AQ is for everyone, but not for 'u' and 'mi'.
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    vinz, has this tallied with your pH/kH readings for any tank of yours?

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    Quote Originally Posted by vinz
    0.5, 0.6... close enough. A drop of 1.7 pH will give us between 30 to 40 ppm of CO2.
    Would it be true if my pH drops by as much as (1.7 x 2) = 3.4, I will get a CO2 level in my tank at about 60 to 80ppm?

    Just curious, as I wish to up my tank to about 50ppm for the first few weeks of setup, no invitation to algae
    *Paranoid*
    Regards,
    Izzat

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    Quote Originally Posted by aCe^bOwleRz
    Would it be true if my pH drops by as much as (1.7 x 2) = 3.4, I will get a CO2 level in my tank at about 60 to 80ppm?

    Just curious, as I wish to up my tank to about 50ppm for the first few weeks of setup, no invitation to algae
    *Paranoid*
    No. A drop of 1.9pH will give you about 45ppm already.
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    Quote Originally Posted by |squee|
    vinz, has this tallied with your pH/kH readings for any tank of yours?
    Are you asking if it tallies with the chart? If so, I haven't checked, and I don't have to. The point is that the chart does not take into account pH that has been skewed by other factors, like ADA Aquasoil. This method does not care. You just determine the starting pH, ie. pH of tank water at ambient CO2 levels (which is assumed to be around 0.5 to 0.6 ppm) and aim for 1.7 or higher drop in pH.

    This target drop is true for any KH as long as it's 1dKH or higher.
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    Quote Originally Posted by vinz
    No. A drop of 1.9pH will give you about 45ppm already.
    Cool

    So if the reading of my aerated tank water is 6.8pH, I will need 4.9pH during the course of photoperiod to get 45ppm of CO2 in the tank?

    Thanks Vincent
    Regards,
    Izzat

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    Quote Originally Posted by vinz
    Are you asking if it tallies with the chart? If so, I haven't checked, and I don't have to. The point is that the chart does not take into account pH that has been skewed by other factors, like ADA Aquasoil. This method does not care. You just determine the starting pH, ie. pH of tank water at ambient CO2 levels (which is assumed to be around 0.5 to 0.6 ppm) and aim for 1.7 or higher drop in pH.

    This target drop is true for any KH as long as it's 1dKH or higher.
    Vinz:

    My 6' tank water sample (after 1 day idle) reading about 6.8 , and with 1.7 reduction of PH to 5.1 That is very low !!! I cranked up the CO2 previously to countless bubbles , and dropped to 5.6 . My shrimp went crazy and some fishes also gusping for air. Only thing was that my plants were very happy as they bubbling like mad.

    Can someone verify this low PH ? Assuming some high demand tank using ADA sand and using ADA diffusor , I don't think the tank PH can reach so low as the CO2 reaction is not good for this type of diffuser. Yet the plants' growth very healthy.

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    Quote Originally Posted by neon
    Vinz:

    My 6' tank water sample (after 1 day idle) reading about 6.8 , and with 1.7 reduction of PH to 5.1 That is very low !!! I cranked up the CO2 previously to countless bubbles , and dropped to 5.6 . My shrimp went crazy and some fishes also gusping for air. Only thing was that my plants were very happy as they bubbling like mad.

    Can someone verify this low PH ? Assuming some high demand tank using ADA sand and using ADA diffusor , I don't think the tank PH can reach so low as the CO2 reaction is not good for this type of diffuser. Yet the plants' growth very healthy.
    I do feel there might be some issues with this method as well. Some pH pens/probes are simply wacky and tends to drift in one direction more readily than the other. You are safer going by the pH/KH method and then adding more CO2 progressively via bubble rate till you get the growth you should get/retard algae growth. Shut the CO2 off at night and make sure you have some surface movement going 24/7 (not alot, just good movement but not ripples). Give the changes sometime (3 days or more) to respond and do the incremental method slowly as well as watching the critters closely for stress signals.

    Neon, drop the diffusor or you would need a couple of it (at least 2) and powerheads near it to move the CO2 around the big tank.

    Regards
    Peter Gwee

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    Hi Peter,

    I am pretty sure that the ADA soil will screw my tank pH value for at least 6 months.
    Terence measured his 1 year old ADA soil setup without CO2 injection and it was pH 6

    I can get pH 4.5-5 without CO2 injection for my new setup, which means that the pH/KH readings might not be so useful?
    I think Vincent's suggestion for me to use Krause method of measuring CO2 is probably the best method with regards to usage of ADA Aquasoil, as I had actually wanted to use lifestock to determine my maximum bps for CO2
    Regards,
    Izzat

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    Or you can go the easy way, pump that CO2 to the point where the livestock show stress at night, then lower it slightly so livestock is comfortable and CO2 injection rate is highest you can go.

    Neon, Amano uses at least 4 of such diffusors at different points in a large tank like 6ft. A reactor will be better for you imho

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    Quote Originally Posted by aCe^bOwleRz
    Hi Peter,

    I am pretty sure that the ADA soil will screw my tank pH value for at least 6 months.
    Terence measured his 1 year old ADA soil setup without CO2 injection and it was pH 6

    I can get pH 4.5-5 without CO2 injection for my new setup, which means that the pH/KH readings might not be so useful?
    I think Vincent's suggestion for me to use Krause method of measuring CO2 is probably the best method with regards to usage of ADA Aquasoil, as I had actually wanted to use lifestock to determine my maximum bps for CO2
    What is your KH level? How much water changes are you doing for the tank? Most aquatic substrates goes back to neutral pH after a month or two once the bacteria takes over and the peat wears off. Regular large water changes removes possible influences from humic acids and peat. Do note that ADA aquasoil lowers the KH down to lower than 1 or zero. Injecting CO2 is going to cause possible pH crashes if that happens and might kill your critters.

    Regards
    Peter Gwee

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