# How much does CO2 affect PH



## waterfaller1 (Jul 5, 2006)

As the title states, is there a way to calculate, or a rule of thumb?


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## Duckweed hunter (Feb 2, 2011)

The more co2 the bigger the drop...I go by my drop checker and a Ph controller

Sent from my PC36100 using Tapatalk


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## penpal (Mar 27, 2010)

Does kh effect the ph drop and reading?


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## Hoppy (Dec 24, 2005)

If there is nothing in the water affecting the pH, except for carbonates and CO2, the equation that describes the effect of CO2 on the pH is:
ppm of CO2 equals KH of the water times 3 times ten raised to the power of 7 minus the pH. But, aquarium or tap water contains other things affecting the pH, such as tannins, phosphates, and various chemicals added to the water by the water department to keep the pH high. Another way to look at that relationship is to notice that it means that if you increase the dissolved CO2 by a factor of 10, the pH will drop by 1.0.


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## Vancat2 (Jun 23, 2010)

http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html


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## Stevenicoloconnor (Feb 21, 2011)

...this is golden!



Hoppy said:


> ... the equation that describes the effect of CO2 on the pH is:
> ppm of CO2 equals KH of the water times 3 times ten raised to the power of 7 minus the pH.


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## plantbrain (Dec 15, 2003)

waterfaller1 said:


> As the title states, is there a way to calculate, or a rule of thumb?


Relative drops can work okay I think.
Even with tannins and what not in the water..........but it is relative.

So eyeballing and slow small progressive adjustments are wise.

Adjust, observe and measure for 3-4 days, adjust a tiny bit and so on.......
I use the needle valve and the rate of CO2 addition, not the pH however. (*Ask yourself why I do this.*)


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## waterfaller1 (Jul 5, 2006)

plantbrain said:


> (*Ask yourself why I do this.*)


Because you are Tom Barr...:icon_ques:tongue:


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## btimmer92 (Mar 12, 2011)

So, Tom, you just make small changes to the bubble count, observe , and repeat?


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## plantbrain (Dec 15, 2003)

btimmer92 said:


> So, Tom, you just make small changes to the bubble count, observe , and repeat?


No, the bubble count is rather imprecise.

A nice vernier handle(these can be DIY with a little paint and add a fat knob etc or buy one etc........) is a better tool for this ona good quality needle valve.
The only other way I know is a mass flow controller, these run about 1200$, but are extremely accurate(should be for the cost).

The rate of CO2 is independent of effects on pH/KH in the tank itself, if you use pH.........this can and does move around, as can KH.

However, the absolute addition of CO2 or the ppm is relatively stable with the valve method. Only degas rates(so keep the tank topped off good) that might change, circulation(you do not want clogged filters etc) or increase/decrease in plant biomass and uptake become the main players(keep tank pruned consistently).

So basic maintenance is more an issue using this method as with any, but not much else once set.


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## waterfaller1 (Jul 5, 2006)

This tank is not a conventional set up.. ie: filter ..etc. I am not sure how effective CO2 might even be. It is a 90 gallon reef ready tank converted to fresh. So, built in overflow, leads to sump, through filter sock, past UV, over media bags w/ Eheim media, over baffle, return by external pump.


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## Hoppy (Dec 24, 2005)

You can modify the reef tank so it will work ok with CO2. Tom can explain that part. And, the reason Tom can adjust CO2 the way he does is that he has loads of experience judging how the plants look, about how much CO2 will be needed, and *how to be observant with a planted tank*. Those of us who haven't achieved that experience yet, can use a drop checker as a crutch to help us get close to having a good level of CO2, instead of fumbling around at low CO2 levels thinking we might be killing our fish. For some people they say courage comes in a bottle, but for planted tank keepers, it can come in the form of a drop checker.


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## waterfaller1 (Jul 5, 2006)

Great analogy. I bow to all of the great green mean machines at TPT!:icon_smil


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