# Using the pH, KH, CO2 chart



## John P Coates (21 Aug 2014)

Hi Folks,

I want to try to gauge the acccuracy of the pH, KH, CO2 chart for determining CO2 concentration in the typical (!) tropical planted aquarium with fish. As I understand it, this chart relies on carbonic acid being the only acid determining the pH of the aquarium water. But there are other acids to consider, one of which is humic acid.

So, in practice, just how accurate are the CO2 figures that it indicates?

JPC


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## ceg4048 (21 Aug 2014)

Zero. It's not only the pH data that is corrupt, but also the KH. See http://www.ukaps.org/forum/threads/ph-pens-and-low-kh.33920/#post-361828

This relationship of pH KH and CO2 only ever happens in a DC, because the only acid in a DC is carbonic acid and the KH is due 100% to Carbonate.

In any other water from tap or from well, the two parameters that are being used to calculate the CO2 content are both corrupt, and that corruption will ALWAYS overestimate the CO2 content.

More details of this relationship explained  here=> http://www.ukaps.org/forum/threads/what-form-of-carbon-do-water-plants-use.26887/#post-279433

Cheers,


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## John P Coates (21 Aug 2014)

ceg4048 said:


> Zero. It's not only the pH data that is corrupt, but also the KH. See http://www.ukaps.org/forum/threads/ph-pens-and-low-kh.33920/#post-361828
> 
> This relationship of pH KH and CO2 only ever happen in a DC, because the only acid in a DC is carbonic acid and the KH is due 100% to Carbonate.
> 
> ...


Hi,

Sorry, what does DC stand for in this context?

If we make up tank water using RO water and then add Ca, Mg and Na carbonates/bicarbonate, does this change the picture at all? (compared with tap water).

JPC


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## Andy Thurston (21 Aug 2014)

Drop checker


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## ceg4048 (21 Aug 2014)

John P Coates said:


> If we make up tank water using RO water and then add Ca, Mg and Na carbonates/bicarbonate, does this change the picture at all? (compared with tap water).


You still have the problem of tank acids. Now you simply have a different overestimate.

Cheers,


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## John P Coates (21 Aug 2014)

ceg4048 said:


> You still have the problem of tank acids. Now you simply have a different overestimate.
> 
> Cheers,


OK, but we're one stage nearer! To what extent do the tank acids affect pH? I'm just exploring all possibilities to see if we can do some meaningful measurements. Wasn't it Isaac Newton who said 'if we don't measure things, then how can we expect to manage them?' (or words to that effect).

EDIT: I was wrong about Isaac Newton. The statement comes from the mouth of Lord Kelvin.

JPC


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## ceg4048 (21 Aug 2014)

Nearer to what? Total meltdown? H+ ion concentration levels have an exponential contribution. More importantly, the acids production in the tank varies.

Did you know that Newtons gravitational theory and equations are completely wrong? He even knew it and came up with phony fudge factors that we still use today to make the answers come out nearer to the truth.

Our fudge factor is to simply measure the pH differences along the photoperiod time line and to use a few rules of thumb to govern the injection rate. That's how we manage them.

If you want to use this chart, and if the KH is 100% due to Carbonate then use the values a couple of blocks into the red zone. That more or less will come closer to accounting for the acid discrepancy and more or less will accomplish the same as the pH profile method:



 

Cheers,


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## John P Coates (22 Aug 2014)

I feel like we're getting somewhere!

It's hard work, though.

I don't know if the above chart incorporates the latest equation, which is:

CO2 = 15.65*dKH*10^(6.37-pH)

JPC


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