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An Old CO2 Idea is a Good New Idea

Discussion in 'CO2 Enrichment' started by VaughnH, Oct 10, 2006.

  1. VaughnH

    VaughnH Lifetime Charter Member
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    I just bought an imitation ADA "drop checker" on ebay, eBay: Type1 Co2 Drop Checker-monitoring proper dosage of CO2 (item 250036844403 end time Oct-14-06 06:06:32 PDT)
    and have started experimenting with it. It seems to work extremely well!

    The secret to using one of these as a CO2 meter and not as a pH indicator is to use distilled water, with KH adjusted to 4.0 with baking soda, in the bulb. At a KH of 4.0, the pH that goes along with that KH when the CO2 is at 30 ppm is 6.6, and at pH of 6.6, the AP pH test kit or any other that uses that indicator, shows an easily recognizable green color. Also, slight errors in measuring KH, say +/-0.1, which is an achievable accuracy by using 4 times bigger water sample, do not affect the reading much. An error in judging the color that is well within practicability is +/- .1, and that error gives a CO2 ppm error such that the 30 ppm may be between 25 and 40 ppm, which is far better than any other method we use. This is great because it removes completely the effect of having odd tank water, with other sources of alkalinity or acidity than carbonates and CO2.

    I set up my "drop checker" with KH=4.0 water, an excess of indicator reagent, which I have found has no effect on the accuracy, but makes judging the color easier, and set it in the tank about 3" below the water surface. It took about 2 - 3 hours for the color to stabilize - unfortunately at yellow! My fish were mostly at the surface gasping!

    I will be continuing to use this, adjusting the bubble rate to keep the indicator color at green and will report back here later about how it is working. Right now, for the first time in months I can see "light at the end of the CO2 measurement tunnel"!
     
  2. neil1973

    neil1973 Prolific Poster

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    Good job VaughnH, and good thinking. It will be interesting to hear how you get on with this.

    A few things occurred to me while reading you post:

    I’m no expert on ph indicator solutions and don’t know how much they vary but it would perhaps be useful for anyone using this method, that has the opportunity, to use a well calibrated ph meter to check at what ph their solution becomes a particular colour. If anyone does this they could post their findings for the benefit of others.

    A lot of people including my self set their maximum CO2 level (bubble rate) by careful observation of the fish. In my case I increase the CO2 slowly and carefully until the fish start showing signs of breathing faster/more heavily and then back it off a fraction so that the fish are breathing normally. Using this method and based on the ph/kh tables (using a well calibrated ph meter) my tank apparently runs at around 90ppm. I think many people using the kh/ph tables are finding that they apparently have even higher levels of CO2. While many fish can almost certainly tolerate considerable more than the often quoted 30ppm it seems likely that as VaughnH suggests the very high levels many are apparently getting is due to the effect of other acids in the water.

    What I think would be interesting would be to try and establish roughly what the CO2 level is in tanks where the level is set as high as possible using observation of the fish. A possible solution here based on VaughnH’s idea would be to establish at exactly what ph the indicator becomes green. Then use a range of solutions at different kh values (e.g. 4, 5, 6 etc) prepared as suggested by VaughnH to establish what kh is needed to achieve a known ph in a tank with maximum amounts of CO2 added based on fish health and consequently the CO2 level in such a tank.

    Cheers
    Neil
     
  3. Tom Barr

    Tom Barr Founder
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    Merely setting the KH at a referenced level, does not mean it's going to stay that way, just like the CO2 level inside the bubble.

    If the CO2 concentration changes inside the bulb, what do you think the KH does inside the bulb?

    You can set the KH correctly, but other organics, hydroxides and tank's KH will alter things over a day or so, maybe less depending on the tank's KH, ionic differences between the solutions.



    Regards,
    Tom Barr
     
  4. VaughnH

    VaughnH Lifetime Charter Member
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    Tom, are you saying CO2 alters the KH? There is no mixing between the solution in the "drop checker" bulb and the aquarium water, so I see no way for the KH to change unless the CO2 does it. When we do the check where we "degas" a tank water sample, then shoot for dropping the pH of that sample by 1.0 in the tank, we are assuming that the KH is not changed by adding CO2.

    How do ionic differences change what is in the "drop checker"? As I understand how this little device works, the air gap between the tank water and the "drop checker" water isolates the two liquids, but CO2 reaches an equillibrium with that air and between the air and the "drop checker" water. So, the assumption is that the ppm of CO2 eventually is the same in both bodies of water.

    Obviously, one day doesn't prove anything, but I don't see how, theorectically, this will not work.
     
  5. VaughnH

    VaughnH Lifetime Charter Member
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    I am getting confused now! I'm not saying this is an unusual condition for me, but.....

    The equation for CO2 in water is: CO2(ppm)=3*KH*10exp(7-pH)

    I am assuming that this equation says that if you dissolve CO2 into pure water there will be an equillibrium reached between the pH and the KH, and the equillibrium values of each depend on the ppm of CO2 dissolved. Is this correct?

    Assuming it is: How can this equation work if the water isn't pure - if it has a non-zero KH when there is no CO2 dissolved in the water? The only way the equation gives a zero value for ppm of CO2 is if the KH is zero.

    So, how can this equation give a meaningful answer if the water has, for example a KH of 10, due to sodium bicarbonate for example, with no dissolved CO2 in it?

    My lack of knowledge in this area is annoying me!
     
  6. Tom Barr

    Tom Barr Founder
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    No, I'm not saying CO2 does anything to KH.

    I am saying the referenced KH you added will diffuse out, just like the CO2 diffuses in.

    That's how these devices work.

    Use the tank's water, not a referenced distilled water and baking soda.

    The water inside these checkers will equilibrate with the tank's water.
    So the KH and other things in the tank will influence the checker over a few hours/day or so etc.

    The CO2 has to get in there to change the color and show that there is a change in CO2 through the day right?

    Same deal here, except in their case, the issue is KH changing to what is inside the tank and diffusing out of whatever small referenced KH solution you added to the checker.

    Not sure if this is clear enough.

    You are not adding KH.
    You are adding CO2.

    The KH will change becuase of the tank's KH and other ions will diffuse into the checker. This will not take that long.

    Then that reference solution in the check will show a different reading.

    I think the idea is good initially, but the reality is that the the KH/checker solution will change rapidly and you may as well just add tank water, not distilled and baking soda etc.

    Regards,
    Tom Barr
     
  7. VaughnH

    VaughnH Lifetime Charter Member
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    This must be a slow brain day for me: how do carbonate ions cross the air gap to go from the tank water to the indicator water - there is no physical contact other than the air gap and the glass surface?

    In a couple of days I will be satisfied with my CO2 bubble rate - I hope, and I will test this with just the 4 degree KH water in the bulb, then recheck it in a few days to see if the KH has changed. My tank water is less than 1 degree KH so the change, if any, should occur pretty quickly.
     
  8. Tom Barr

    Tom Barr Founder
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    Opps, air gap, I was worried you'd say that:eek:
    Then there should not be any issue in that case.
    Some of the checkers come in contact with the tank water.

    This will work well and is a VERY good idea in that case.
    I'm the one with the slow brain day:D

    Regards,
    Tom Barr
     
  9. VaughnH

    VaughnH Lifetime Charter Member
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    That's a relief - I can tear up the high school enrolment papers now!

    Next issue: does anyone know if the indicator (dye) fades with continuous exposure to aquarium light intensity? My indicator is a greenish golden color now - meaning about 45 ppm of CO2, but it is not intense enough to satisfy me, and I have about 12 drops of reagent in the mix. (I'm using the Aquarium Pharmaceuticals reagent instead of the tiny bottle of stuff that came with the device.) Maybe I should try the cheapy reagent next. It seems like there would be a maximum amount of reagent you could mix with the water without changing the chemistry - I think it has sodium hydroxide in it.
     
  10. VaughnH

    VaughnH Lifetime Charter Member
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    My little drop checker is working great now. I have adjusted the bubble rate a few times and am now keeping the checker color on green from about an hour after the CO2 comes on until it goes off. Here is a photo of it in the tank - green!

    [​IMG]

    I see no signs at all of the fish being stressed by the CO2. So, my next step will be as Neil suggested - change the indicator solution to KH=5, which will make it be green at 40 ppm. Then I will watch to see if the fish have any problems at that ppm. If not, and after a week or so, I will try KH=6, which gives 45 ppm when the color is green. I keep wondering if we reallly know what the maximum CO2 concentration can be without bothering the fish, since I don't know how anyone knew what their concentration was using the methods we had to measure it. And, is there any theoretical way to determine what is too much for the fish? I do know that 70 ppm+ is too much because I had that briefly when I first started using this device and all of the fish were gulping air at the top.
     
  11. Tom Barr

    Tom Barr Founder
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    Well that is the Achilles heel with this method, you need to know what the CO2 is for that particular color change. the other issue is really accuracy, some is better than none mind you, but when it's green, is it 30-50ppm?

    Or 35-45 ppm?

    Or 38-42 ppm?

    How accurate is that color change?
    How accurate are our own eyes to such colormetric changes?

    This part needs to be clear.
    I like this method BTW, it's a very good one and revists on old device that's easy for new and experts alike to use.
    But the idea of using a ref solution vs tap or tank water is very wise and could be sold even, the KH ref water solutions that is:).

    Regards,
    Tom Barr
     
  12. VaughnH

    VaughnH Lifetime Charter Member
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    I think the accuracy with KH=4.0 water is from 25 to 40 ppm for when it is green. You can see the difference, but not really easily between pH of 6.6 and 6.5, as well as 6.6 and 6.7, and the KH can easily be set to 3.8 to 4.2 degrees, so at KH 4.2 and pH 6.5 the ppm is 40, and at KH 3.8 and pH 6.7, it is 23 ppm. I think that is the biggest error you can have, and that is much, much better than any other method I know about. For example, the degassed 1.0 pH drop method gives results of about 5 to 50ppm, depending on just how much CO2 remains in the degassed sample.

    I assume that the makers of these little devices don't really know about using them this way, or they would package with the device, a bottle of KH4 water, containing the indicator reagent, and a cheap syringe with a curved tip for squirting the fluid into the bulb easily. It seems like the obvious way to sell it, and their sales would be much better then. They could even add a color band having the proper green color so setting it would be more accurate. Right now it's like inventing the automobile and selliing it as a way to pull wagons.
     
  13. Tom Barr

    Tom Barr Founder
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    Well, the accuracy and then some clowns will go out and think they have the same accuracy and toss some baking soda into some water, might not even be RO/Distilled/DI, etc, kill their fish and then cry and say it's a bad method etc.

    That's going to happen.

    But if you stress the critical aspect here, the need for DI water, reference KH's with good accuracy, rinsing before/after you change the solutions etc inside the flask with DI water 3x, and realize there is a range of CO2 ppm the flask will yeild, then you have a good explaination and how to that you can refer back to should these colowns think theycan just wing it.

    Brand specifics are important also, you might want to try several common brands.

    Some one will try one brand that targets 15ppm for green, another that will target 30ppm for green and so on..........

    Need to get everyone on the same page that plans on using this method and also, most are not the best when it comes to making a reference KH solution let alone NO3 ref solutions etc.


    Regards,
    Tom Barr
     
  14. cousinkenni

    cousinkenni Prolific Poster

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    Instead of adding some NaHCO3 to water and testing the result....... is there some way to add a standard amount of NaHCO3 to a standard amount of water to get the KH of 4 we desire?

    I guess I am just not sure of the conversion of ppm to dKH. I know for CaCO3 it is a conversion of 17.86 or something like that, but does that apply to NaHCO3?

    I guess this is for all those people that have access to analytical balances.

    So for 4dKH I would need 71.43ppm or 71.43mg/L(assuming 17.86 ppm/dKH).
    If I use a volume of 1L that means I would need 71.43mg of CO3.
    To get 71.43mg of CO3 I would need 98.36mg of NaHCO3 or .09836g.
    I would then add .09836g to a volumetric container and fill to 1L with ddH20 to get KH4.


    Is this correct? Am I missing something in the conversion or the dissociation of NaHCO3 to HCO3-1 or CO3-2?

    I feel measuring out a specific weight should be more accurate then adding some and then testing. Since I have a scale at my disposal I would rather do it this way. I just want to make sure my calculations are correct before proceeding.


    Thank you for your time,

    Ken T.
     
  15. Professor Myers

    Professor Myers Guru Class Expert

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    Vaughn, How's your drop checker working out ?

    Has this allowed you to refine your Co2 administration as you had hoped ? Have you made any refinements to this method ? Any new Epiphanies ??? This is solid stuff ! Prof M
     
  16. Tom Barr

    Tom Barr Founder
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    Hopefully over the Xmas break I'll make a pH probe version and illustrate it here.

    Regards,
    Tom Barr
     
  17. Tom Barr

    Tom Barr Founder
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  18. cousinkenni

    cousinkenni Prolific Poster

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    So Tom,

    even with the 5.5% w/v Sodium bicarbonate reference solutions, how does that relate over to dKH or ppm?

    Thanks,

    Ken T.
     
  19. VaughnH

    VaughnH Lifetime Charter Member
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    I couldn't be more pleased with my little drop checker. I like the looks of the glassware to start with. I have changed the KH that I use to 5 dKH, which means green will be about 40 ppm instead of 30 ppm. I have adjusted the bubble rate a couple of times when the color seemed more blue green than green, so it is acting as the monitor I wanted. When I replaced my Barr Internal Venturi reactor with a more sturdy one this allowed me to see if it was working well at the bubble rate it started out at - it was.

    All that remains, as far as I am concerned, is to try a 6 dKH solution, which would give 45 ppm at green. I am still monitoring the effectiveness of my GDA clean up so I don't want to introduce that change just yet. Also, I'm wondering how I would be able to use a pH probe stuck in one and left in the tank without it being in the way of the hood. I doubt going down that road, but it would certainly improve the accuracy of this method.

    I sent an email to the guy in Hong Kong who sells the glass ones on ebay suggesting he read the APC thread about these, and that he consider packaging a 4 or 5 dKH premixed with indicator solution with his. No answer yet.
     
  20. Tom Barr

    Tom Barr Founder
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    I have a very simple and effect pH probe design for this.
    A trip to Tap plastics and a drill will do the rest.

    Regards,
    Tom Barr
     
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