# CO2 drop checkers



## Phil Edwards (Jan 22, 2004)

What exactly is the premise behind the drop checkers that I'm seeing all over the place? Are they basically suspended titration chambers that react when CO2 gas evolves out of the water column into the checker device? 

How often do the reagents in the device need to be replenished and how long does the typical amount of reagents that come with a device last before they run out?

Thanks,
Phil


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## Bunbuku (Feb 10, 2008)

Yes, the dye is bromothymol blue which is a pH indicator http://en.wikipedia.org/wiki/Bromothymol_blue for titration. The globe is filled with a 4 dkH solution and allowed to equilibrate with the tank water. Then the pH/color of the solution depends on CO2 levels in the tank water. The color can be used to infer CO2 levels using this page is http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm. I adjust the bubble rate to achieve a light green to yellowish-green color.


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## orlando (Feb 14, 2007)

Hopefully this will help  If you scroll down to the bottom you can check it out 
http://www.greenleafaquariums.com/planted-aquarium-blog/

-O


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## Phil Edwards (Jan 22, 2004)

*********
<edited to remove a joking statement that didn't transcribe well to text.>

How long do the reagents in the counter last before needing to be replaced? Typically, how long does the amount of reagents sent with a drop checker last before they run out?

Thanks for the link. That's just what I wanted to know.


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## orlando (Feb 14, 2007)

I haven't changed my fluid in over 3 months, still works fine till this day. I would think the bottles they come with should last well into one year 

Regards, Orlando


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## wet (Nov 24, 2008)

Anybody know the +/- for CO2 off hand for the color? For example, with 4dKH will the good color range be from 20-40ppm CO2? If I used say 6dKH would it be from 35-55ppm CO2? Is there a formula?

Thanks.

I'm thinking of building a calc for the Double Check Cal Aqua ones where the second drop checker is not a reference but rather lets one get a better idea of their ppm using upper and lower thresholds for each sample.


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## chagovatoloco (Nov 17, 2007)

The man who came up with the idea has not posted for a while, what happened to hoppy?


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## Bunbuku (Feb 10, 2008)

wet said:


> Anybody know the +/- for CO2 off hand for the color? For example, with 4dKH will the good color range be from 20-40ppm CO2? If I used say 6dKH would it be from 35-55ppm CO2? Is there a formula?
> 
> Thanks.
> 
> I'm thinking of building a calc for the Double Check Cal Aqua ones where the second drop checker is not a reference but rather lets one get a better idea of their ppm using upper and lower thresholds for each sample.


See my 2nd link to Chuck's Planted tank page. In the middle of that page you will see a calculator that you can use to estimate CO2 if you know the pH and kH. The color thing will be considerably harder to "calibrate" as there so many variables in what goes into the human perception of color.
If one really wants to know precisely, you should probably use a pH probe and a spectrophotometer. See this page http://paws.wcu.edu/bacon/Ka-BTB.pdf

Phil:
I don't have a precise answer for you on how long the dye remains "effective". I do know that I am still using my original 5 ml dropper bottle from my ADA drop checker after 1 year. I change my solution about month not bec it has stopped working (it still turns blue overnight when I have the pipes in aeration position), but because I need to clean the algae and other crud building up on the suction cup and glassware.


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## wet (Nov 24, 2008)

> See my 2nd link to Chuck's Planted tank page. In the middle of that page you will see a calculator that you can use to estimate CO2 if you know the pH and kH.


Right: For clarity, if we expect the 4dKH standard to turn green with the 30ppm CO2 standard/rule of thumb, the values above is for 45ppm CO2 with a 6dKH standard +/- 10ppm. Happen to know if the color thing is at least a linear relationship or does it go exponential?


> The color thing will be considerably harder to "calibrate" as there so many variables in what goes into the human perception of color.


I don't think this is so important, but have never used a drop checker. The idea of using a Double Check Cal Aqua unit (or two standard drop checkers) from Orlando is simply to leverage a design with a reference sample (which is a great idea) to two different standards where you can use the maximum range for sample 1 and the minimum range for sample 2. Or even the "Too High" and "Too Low" colors. Its a better guess/estimate without the cost nor trouble of a more precise measurement.

Hoppy still posts on Barr's forum. I will refine this idea and post there for his critique, but when up for it I'll look through his posts too. He's so methodical he or Salt or someone probably has the formula posted in some thread. But if someone has it already, I'll make you the web calc for it 

Or is this idea off base? If we agree the range of drop checkers is good enough for our purposes, I think we can also agree a tighter range from an inexpensive unit would be even better. Or is there another reason its a bad idea?

******** I am dumb: from Greenleaf's pics the Double Check unit from Cal Aqua clearly doesn't equalize gas in the second/reference sample. I just missed this until now.


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## Bunbuku (Feb 10, 2008)

wet said:


> Right: For clarity, if we expect the 4dKH standard to turn green with the 30ppm CO2 standard/rule of thumb, the values above is for 45ppm CO2 with a 6dKH standard +/- 10ppm. Happen to know if the color thing is at least a linear relationship or does it go exponential?


It's exponential for sure - that is because the principle is based on the H-H equation. See the link to the chemistry page on my earlier post. In the figures of the absorbance vs pH, it's an S-shaped curve


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## Phil Edwards (Jan 22, 2004)

Hey Orlando, what happened to your posts? I sure hope you didn't think I was serious. 


Sometimes I'm a numbnut and forget how poorly my sense of humour comes across online.


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## orlando (Feb 14, 2007)

Oh man  I thought I was in trouble or something.. 
Thanks Phil! Lol! I can fix it! 
http://www.greenleafaquariums.com/planted-aquarium-blog/
If you scroll down, I tried my best to discribe how this little gizmo works. 

Thanks Phill! Orlando


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## wet (Nov 24, 2008)

'case anyone else is interested in the using multiple drop checkers idea earlier, or wants to adjust their drop checker/KH reference for a target ppm, here's a calc: http://wet.biggiantnerds.com/drop_calc.pl

Here's a thread where we can talk about ideas without messing up Phil's thread: http://www.aquaticplantcentral.com/forumapc/showthread.php?p=440257#post440257


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