PH/KH state my co2 is 30ppm when I am not adding co2 at all - The Planted Tank Forum
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post #1 of 7 (permalink) Old 03-19-2019, 07:39 PM Thread Starter
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PH/KH state my co2 is 30ppm when I am not adding co2 at all

Ph is 7.1 and kh is 9 in the morning before light and co2 turn on. If I follow the traditional ph/kh charts, then I'm already at 30ppm co2 which makes absolutely no sense.


I back this up with the color changing tester in the tank. I definitely need to be in the low 6's to hit 30 ppm. My KH is 9 because of large rocks in the water. I use RO water and it drops to around 4 or 5 when I do a 50% water change.


What is going on here? Am I missing something obvious with my tank?

Last edited by Ddrizzle; 03-19-2019 at 08:15 PM. Reason: edit
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post #2 of 7 (permalink) Old 03-19-2019, 10:02 PM
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Are you saying that your CO2 tester is also showing around 30ppm?

The charts are unreliable in determining actual CO2 levels, as there are many other factors than just CO2 that affect PH. IMO, the charts are worthless.
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post #3 of 7 (permalink) Old 03-19-2019, 10:04 PM Thread Starter
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Yeah, I'm saying the chart makes absolutely no sense with my parameters. It says I have about 30ppm of co2 when I am literally not injecting any co2 during that time.

To get to 30ppm via the color changing test in the tank, I need to inject co2 and be around 6.3 ph. However, my fish also start gasping so I'm not sure what to do.

Last edited by Ddrizzle; 03-19-2019 at 10:05 PM. Reason: edit
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post #4 of 7 (permalink) Old 03-19-2019, 10:47 PM
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Just plugging in your tank KH and PH doesn't tell you how much CO2 you have. if you just take a glass of your water and let it site or a few days all there will be no significant CO2 in it but the KH and PH will be about the same. So in your case 30ppm is your zero point. Now add CO2 and remeasure your PH. Now using the chart with the new PH value determine your new value. Then subtract 30ppm from the new value to gee your actual CO2 level.
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post #5 of 7 (permalink) Old 03-19-2019, 10:57 PM Thread Starter
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Ok, this makes sense. Thanks! Looks like I need around 6.6 or 6.7 instead of 6.4 so that's a plus for my fish.
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post #6 of 7 (permalink) Old 03-22-2019, 11:30 PM
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Question

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Originally Posted by Ddrizzle View Post
Ph is 7.1 and kh is 9 in the morning before light and co2 turn on. If I follow the traditional ph/kh charts, then I'm already at 30ppm co2 which makes absolutely no sense.


I back this up with the color changing tester in the tank. I definitely need to be in the low 6's to hit 30 ppm. My KH is 9 because of large rocks in the water. I use RO water and it drops to around 4 or 5 when I do a 50% water change.


What is going on here? Am I missing something obvious with my tank?
The chart has misled more people than I beleive it has helped.
Contrary to its presentation it does not take into account your starting and ending pH values.
It ASSUMES you have RODI water with the appropriate levels of bicarbonate added to it and nothing else, so it assumes your starting pH and then based on your end pH and kH estimates how much CO2 was injected.

You cannot have stable CO2 levels easily with a changing kH it will make it very difficult, theoretically you could add far more CO2 to your system than would be healthy for any fauna if the acidic water is dissolving your rocks.
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post #7 of 7 (permalink) Old 03-22-2019, 11:35 PM
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It made no sense when the charts showed my fish were in 80PPM of CO2. There are times when we really do need to look for different methods!!
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