# Best way to measure CO2



## zdam20 (Mar 8, 2009)

I have a pressurized CO2 system that I have hooked up to a ph controller to turn the CO2 on + off to control the ph. I've been using the CO2-KH charts to tell me how much CO2 I actually have in my tank. I did some searching locally and nobody has a CO2 test kit. Are the charts good enough if I closely moniter and dose for my kh value? I've got the kh test kits. Thanks for looking.


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## TAB (Feb 7, 2009)

CO2 tests are not very accurate. The chart is fine.


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## Bert H (Mar 2, 2004)

Your most accurate method will be the drop checker.


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## zdam20 (Mar 8, 2009)

I was thinking of diying a drop checker. I guess I'll have to give that a try.


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## chagovatoloco (Nov 17, 2007)

The drop checker only works if you use 4dkh water inside it.


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## orlando (Feb 14, 2007)

This may help clear some air regarding the drop checker. 
I hope its clear 
http://www.aquaticplantenthusiasts.com/showthread.php?t=4

Regards, Orlando


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## Newt (Apr 1, 2004)

The chart is only good if you have low phosphate levels and accurate test hits for pH and KH.


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## zdam20 (Mar 8, 2009)

Thanks for the input everybody. Any idea where I can buy 4 dkh reference solution from?


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## Shad0w (Nov 13, 2006)

you can make your own 4dkH solution using baking soda and kH test kit


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## Newt (Apr 1, 2004)

zdam20 said:


> Thanks for the input everybody. Any idea where I can buy 4 dkh reference solution from?


Orlando has some nice drop checkers and dKH solution at www.greenleafaquariums.com

:fish2:


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## agy (Sep 18, 2009)

1)4dkh solution need 
2) if aquarium water 4-5dkh then measure ok

I prefer better option ph meter or ph controller and then simply look how react stock and plants
Also ph is more important as little + or - co2, ph can drop due some other factors and Dead fish in rsult


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## Aquaticz (May 22, 2009)

FYI
There is a guy on ebay selling drop checkers for a few dollars each. I bought three & they work great. I did have to use suction cups from my supplies as the one they sent was to small to attach to the drop checker


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## Jeffww (May 25, 2010)

No, you don't make your reference solution with your KH test. You test your KH test against the reference solution.

You can make one by dissolving 716ppm baking soda into distilled water then dissolving that to 9 parts of distilled water. 
Use this:
http://www.cnykoi.com/calculators/calckh.asp

Azoo makes a cheap drop checker it also comes with a reference solution.


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## Left C (Jun 14, 2005)

agy said:


> 1)4dkh solution need
> 2) if aquarium water 4-5dkh then measure ok


No. You can't use aquarium water even if the KH is in the ballpark. The pH/KH/CO2 relationship is only good with baking soda as the only buffer. Tannins, other acids and bases in aquarium water throw this out the window.

Check out what Newt and Jeffww are saying.

link: http://www.aquascapingworld.com/magazine/July-2008/July08/Measuring-CO2-pH-KH-Relationship.html



agy said:


> I prefer better option ph meter or ph controller and then simply look how react stock and plants
> Also ph is more important as little + or - co2, ph can drop due some other factors and Dead fish in rsult


Nope too. The pH is not nearly as important as the TDS and CO2/O2 levels. Fish can easily tell what the TDS are as well as the CO2 and O2 levels. They really don't care about the pH. It's the factors that control or make the water a certain pH and TDS that is important to them.


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## agy (Sep 18, 2009)

Left C said:


> No. You can't use aquarium water even if the KH is in the ballpark. The pH/KH/CO2 relationship is only good with baking soda as the only buffer. Tannins, other acids and bases in aquarium water throw this out the window.
> 
> Check out what Newt and Jeffww are saying.
> 
> ...


 I mean not use aquarium water but if You wanna Your drop checker is correct with Yours baking soda solution then need in aquarium kh 4-5 , then measure is ok. 
If in aquarium water will be like kh 8 and in yours drop checker with soda solution 4 kh i think measure will be wrong
I think ph, gh, kh and using chart is more correct for co2
About O2 100% You are right - every body need O2 
Drop checker good for Japans, i found info in net - they see millions colors more as white people.
I think is impossibly to see difference on 6.6 and 6.8 from drop checker color, or simply i don't remember what's green tonality been before 
Maybe I'm wrong


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## Elohim_Meth (Nov 4, 2007)

Jeffww said:


> You can make one by dissolving 716ppm baking soda into distilled water then dissolving that to 9 parts of distilled water.


It gives 71.6ppm of baking soda. I've got about the same amount having done a math. But:


Jeffww said:


> Use this:
> http://www.cnykoi.com/calculators/calckh.asp


1 liter is 0.264 gallon, right? I put 0.264 in Gallons field, 4 in DH change field and get 0.1 g! 
And yet more funny, I've done the reference solution experimentally and I've got the same, 100 ppm of baking soda gave me 4 dkH.


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## jdigiorgio (Jan 29, 2004)

NEWT,

What doyou mean the drop checker will only be accurate with low PO4 levels? What is the correlation?


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