# pH/KH/CO2 chart - reliability



## mysiak (Jan 17, 2018)

I was wondering what CO2 levels I could have in my natural planted tanks and I remembered that there exists this nice chart.

I don't know if I missed something or my water test kit (test stripes) are so wrong, but per the chart I have ~40-50ppm of CO2 which sounds odd. Shouldn't be fish showing heavy discomfort at these values? Also it should be "plants heaven" at these levels of CO2, but I still can grow only "easy" plants. I am going to order fresh test kit, but it will take a few days to arrive. Is there another explanation..?

For the second tank it's about 25ppm of calculated CO2, which sounds a bit high as well, but at least it's safe value.









Source: https://gregthecrazyfishguy.files.wordpress.com/2010/09/screen-shot-2010-10-05-at-5-00-45-pm.png


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## mistergreen (Mar 3, 2007)

It's only reliable if you have very soft water and nothing in your tank that influence the pH & kH like driftwood, dirt, rocks, etc... a drop checker is more reliable since it's a controlled liquid (4dkH) in the drop checker but I doubt it's readable in a dirt take with less than 20ppm of co2.

There's also a co2 test kit that's more accurate
https://www.hannainst.com/hi3818-carbon-dioxide-test-kit.html


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## hoppycalif (Apr 7, 2005)

mistergreen said:


> It's only reliable if you have very soft water and nothing in your tank that influence the pH & kH like driftwood, dirt, rocks, etc... a drop checker is more reliable since it's a controlled liquid (4dkH) in the drop checker but I doubt it's readable in a dirt take with less than 20ppm of co2.
> 
> There's also a co2 test kit that's more accurate
> https://www.hannainst.com/hi3818-carbon-dioxide-test-kit.html


Drop checkers can measure very low CO2 levels if you use low KH water in them:


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## mistergreen (Mar 3, 2007)

Ohhh, that makes sense but it'll be hard to make a low dKH solution, maybe. It might be easy to get a known 4dkH and add known volumes of distilled water to divide the dkH to the desired dkH.


I'd go with that CO2 test kit though.


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## mysiak (Jan 17, 2018)

Thank you gents, that explains it. I'll read more about drop checker method and look around for dedicated CO2 test as well. Once the virus outbreak is over, I will probably order what's cheaper from eBay/ali.


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## zolteeC (Dec 26, 2017)

Ms. Walstad mentions in her book that she used LaMotte® Carbon Dioxide Test Kit. It costs around 45 USD and it has a 1 ppm resolution between 0-50 ppm. More accurate details on the LaMotte website.
I would be very interested to see similar measurements on NPTs to the one the book shows. (CO2 level vs time after lights switched on)


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