# New method for finding CO2 concentration



## holocron (Mar 12, 2006)

I was browsing around APC and noticed a post about a better method of testing the CO2 ppm in a tank. The current known method is to follow the ph/kh relationship, but in some cases that method is thrown off (by adding peat or driftwood for example). So the person made a chart based on the difference between the ph reading of hte water in the tank vs. the ph reading after the water had been sitting out in the open air for 24 hours. The change in PH would determine the co2 concentration.

here is the chart:
http://www.aquaticplantcentral.com/gallery/showimage.php?i=2920&c=3

The whole article:
http://www.aquaticplantcentral.com/...rtilizing/14281-another-co2-chart-to-try.html


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## Plant Crazy (Mar 24, 2006)

Thanks for forwarding that link holocron. It makes a lot of sense, since the pH change in the equilibrated aquarium water can only be due to the CO2 which has now degassed. Unfortunately as they say, the time this takes, is the only drawback. 

I have a pH monitor in my tank, which is left on 24h a day. My KH remains quite stable, so I look at my pH reading to get a ball park estimate of my CO2 concentration. I've found that pH 6.8 works out to be about 30-35 ppm CO2 in my tank. This is probably the quickest way to monitor CO2 (remembering that a stable KH is a prerequisite for this). In fact, the Dupla or Sera 'visual CO2 indicators' work under this premise.

Stan.


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## holocron (Mar 12, 2006)

No problem Stan,

Time is definitely the trade off there, but it at least confirmed that I had the proper amount of CO2 in my tank. I use a visual indicator and from time to time I question its accuracy (more like daily), but this second test confirmed that it was actually spot on.

-matt


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## aspen (Mar 25, 2006)

which co2 indicator do you use? 

i saw them in the stores and was wondering about them.

rick


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## Plant Crazy (Mar 24, 2006)

I previously had a Dupla visual CO2 indicator which I had used for my 10g planted tank awhile back. The visual CO2 indicator solution is the same indicator as the one in the Aquarium pharmaceuticals pH test kit (orange colored indicator).



aspen said:


> which co2 indicator do you use?
> 
> i saw them in the stores and was wondering about them.
> 
> rick


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## holocron (Mar 12, 2006)

I use the red sea one they sold at big als. Its soso, overall it works.



aspen said:


> which co2 indicator do you use?
> 
> i saw them in the stores and was wondering about them.
> 
> rick


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