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Discussion Starter #1
Until recently I thought the co2 chart was what it says even if your not injecting co2. But a good friend explained to me that if your not injecting co2 than it doesn't mean anything. Well I am injecting co2 at about 2 bps. So now how does that translate into the chart. Does my ph/kh have to change before the chart is accurate. Is there a test kit for co2 or just that thing you put in your tank and the color changes to not enough, good or too much?
 

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Just that thing that changes color. It's called a drop checker. It's the best way to have an accurate record of your CO2 since the solution is standardized with a set kH.
 

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The CO2 vs pH/KH chart works whether you inject CO2 or not, but only if the water you are checking has only carbonates affecting its alkalinity and only CO2 affecting the acidity. That keeps the table from being accurate for most aquarium water, but it is accurate for a drop checker with known KH distilled or DI water in it.
 

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Discussion Starter #4
Forgive me for sounding a little naive, but what exactly would be the definition of the carbonates you speak of that affect alkalinity?
And you said that the co2 chart IS accurate to the amount of co2 in the water even if your not injecting co2?
You might need to spell this one out a little for me.
 

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If you take distilled or DI water and add sodium bicarbonate (baking soda), you are adding carbonates to the water. Now if you measure the KH and the pH, you will be able to use the table to determine how much CO2 is dissolved in the water, and it will probably be about .5 to 4 ppm. That is from atmospheric CO2 dissolving into the water. If you take a piece of airline tubing and use it to blow bubbles in that water for 15 minutes (don't pass out!), then measure the KH and pH again, you will probably find about 10 ppm or more CO2 in the water. Those will be accurate measurements, or at least as accurate as you can measure the pH.

Now if you take tap water, which may have phosphates added to raise the pH, put it into the aquarium where a piece of bogwood is seeping out tannins, and then try to measure the KH and pH to determine how muchCO2 is in the water, you will likely get a number around 50+ ppm, even if you aren't injecting CO2. That number wont be correct because the phosphates and tannic acid are affecting the alkalinity and acidity.

That's why a drop checker with distilled or DI water in it will give an accurate measurement of CO2, but not if tank water is in it.
 

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so you are saying the co2 chart is **** unless you have a drop checker?
 

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there's also the method of checking the ph of the aquarium water.. and then let it sit in a cup for 24 hours. Then check the PH again.
the difference is the CO2 dissolving into the water that has gone into the air.
I think .1 difference of PH is 3 PPM of CO2.
 

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there's also the method of checking the ph of the aquarium water.. and then let it sit in a cup for 24 hours. Then check the PH again.
the difference is the CO2 dissolving into the water that has gone into the air.
I think .1 difference of PH is 3 PPM of CO2.
Unfortunately that method isn't accurate either. It depends on the degassed water having 3 ppm of CO2 in it, but when you do some experimenting you will find that there is no good way to know that you have that much CO2 left. If you let the water sit long enough the ppm will drop to around .5. And, if it only sits for a few hours it may be well above 3 ppm. The 1 pH unit difference means the tank has ten times as much CO2 as the degassed sample, which would be 30 ppm if you could assure your self that your degassed sample really has 3 ppm in it.

So, that leaves the drop checker, used with known KH DI or distilled water in it as the only available accurate way to measure CO2. Fortunately this is a cheap device, if you get the Red Sea unit, or make one, and it works very well, as long as you can accurately see the green color.
 

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Discussion Starter #11
Well I have always had a drop checker just never put it in because I hate having things hanging in the tank. But I put it in. blue is low, yellow is high and green is good. I have bluish green. So thank you for all the facts.
 
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