How Accurate are the CO2 Calculators?

KarlTH, please let me know if I'm on the right track in terms of my understanding of the bicarbonate system. In order for plants to grow efficiently they require among other things a carbon source of which CO2 is easiest for the plants to consume. That being said, if the CO2 levels fall off, plants will start to utilize carbon from KH which will lead to an increases in the PH. Therefore in order to prevent fluctuations in PH its necessary to keep levels of CO2 at a constant level or utilize a "bicarbonate buffer" to increase KH.
At present I do not use/dose a bicarbonate buffer would it be wise for me to start considering a DIY CO2 system?
Again thanks again for your insights. Cheers
 
oblongshrimp thanks for the heads up!! Do you know if commercially purchased drop checkers come prepared with the KH solution included?
Thanks and Cheers
 
You do not need to add a buffer. The point about buffers is simply that the tables assume that bicarbonate is the only one in use. In some cases that assumption is way off base. Yours may be such a case.

There is such a thing as biogenic decalcification, which is what you're referring to, but adding a buffer doesn't prevent it. Having sufficient CO2 does. Only a few plants can do it anyway.

Plants require CO2. Any other carbon source needs to be turned into CO2 before the plant can use it. Biogenic decalcification is one way in which a few plants can turn another carbon source into CO2.

The bicarbonate system I refer to is an equilibrium which always exists in any water to which CO2 is added:

CO2 + H2O <=> H2CO3 <=> H+ + HCO3-

These three are in an equilibrium. Of these, HCO3- is bicarbonate, i.e. KH. If you add CO2, then the equilibrium will shift to the right, which you will see ends up releasing H+ ions and therefore lowering the pH. Adding bicarbonate will push the equilibrium to the left, causing H+ ions to be taken up, lowering the pH. That, in a nutshell, is the bicarbonate system, and it has a fixed relationship between KH, pH and CO2 concentration.

If there are other acids present, then the overall pH of the water will be lower than the pH predicted purely by the bicarbonate system. If there are other buffers, then the pH will be closer to the equilibrium pH of those buffers than it would otherwise be. Additional acids are usually the issue in aquaria; organic acids from metabolism, tannic acid leached by peat and bogwood, and so on. Hence pH tends to be lower than the bicarbonate system alone would result in, and CO2 calculations come out higher than the real figure.
 
KarlTH thank you so very much for this very detailed explanation on the bicarbonate system and its relationship to PH, KH and CO2 I'm sure others will benefit as well.
In terms of additional acids you mentioned, I do have grape vine trunk as my "driftwood/bogwood" which I assume could probably leach tannins although I do not visually see any tannins in the water column (i.e. the tint in the color of the water). What in your opinion would be the best way for me to determine my true PH? I suppose I can start by measuring the PH of my water source but then that would not take into account the "acid factor". I hope I'm wrong but I guess the only way to calculate the true PH would be to remove the CO2 from the aquarium for about 24 hours which I'm guessing is probably not a good thing for the plant.
I look forward to your thoughts and or comments.
Thanks and Cheers
 
DAVIDFBT thanks for the link.
Cheers
 
You are measuring the true pH. What it doesn't allow you to do is determine the true CO2 concentration. You'll need a drop checker with pure water of known KH (i.e. no acids or buffers other than CO2 and bicarbonate) to do that.
 
on a side note:
(good description and explanation on the CO2 issues Karl.)

"I do have grape vine trunk as my "driftwood/bogwood" "


word of caution.. grapewood is one of the woods which may deteriorate rather quickly in the tank.
 
KarlTh said:
You are measuring the true pH. What it doesn't allow you to do is determine the true CO2 concentration. You'll need a drop checker with pure water of known KH (i.e. no acids or buffers other than CO2 and bicarbonate) to do that.
Click to expand...

Thanks for the confirmation looks like I will need to go out and find me a drop checker!!

Cheers
 
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