# KH vs. pH - CO2 target ...



## Milan (Jul 6, 2005)

I've never been able to achieve 30 ppm of CO2 in my tank. I have a DIY CO2 with power reactor, which I would assume is working correctly (plenty of CO2, all dissolved), and is running arround the clock. The problem in mind sits in tap water pH and KH not allowing higher concentrations of CO2. Here are the numbers:

Tap water: KH=6; pH=8.0

After CO2 injection: KH=6; pH=7.1

This gives about 18 ppm of CO2. 

Now, what should I do? There are two ways ... If I lower the tap water pH by adding acid (ie vinegar), that would kill the KH, and if I up the KH (ie adding baking soda) that would pull the pH up as well. No win, no win situation seemingly, but one of these ways may work, depending on what is influencing CO2 concentration more. pH or KH? I would like to avoid using RO water, if possible.


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## brad (Jul 10, 2005)

reducing your ph without altering your kh doesn`t add co2. I doubt adding vinegar to your tank would be a good idea anyway. Also, raising kh will raise ph. You can`t simply add baking soda to increase kh and expect your ph to stay where it is. that will not help add co2.


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## JimM (Aug 26, 2005)

as far as I understand it the KH and pH relationship is only used as an indicator of co2 levels, they do not effect the amount of co2 being dissolved into the water.. 

you could try to decrease surface agitation or increase the efficiency of your reactor somehow.. 

I could be wrong, HTH.


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## Milan (Jul 6, 2005)

I know altering pH or KH would not add CO2, but my question was would it help dissolve it better ...


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## Milan (Jul 6, 2005)

JimM said:


> ... you could try to decrease surface agitation or increase the efficiency of your reactor somehow..


Although I have a HOB filter, surface agitation is minimal (next to nothing) due to a slight design modification on it. Reactor does not spit any bubbles out, and there is plenty of gas produced, so I would assume there is nothing to be improved here ...


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## dennis (Mar 1, 2004)

If surface agigation is minimal and reactor is working at peak effeciency, then you must increase CO2 output from your DIY mix. Try running 2 generators and change the batch in only one each week, alternating bottles each week. You can also try a different reciepe for a higher CO2 output. Adjusting the water parameters should have little effect on how much CO2 gets dissolved. The answer lies in your Co2 production methods. You could also switch to pressurized or go the paintball method.


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## imatrout (May 12, 2005)

I am under the impression that adding baking soda to raise KH will NOT raise your PH.

http://rexgrigg.com/waterchem.htm


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## dennis (Mar 1, 2004)

It will I have added baking soda to my tank and watched the pH controller reading climb in line with the CO2 concentration used for kH-Ph relationship charts.


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## Milan (Jul 6, 2005)

dennis said:


> ... or go the paintball method.


What is "paintball method"?


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## imatrout (May 12, 2005)

Dennis,

I'm surprised that's what you saw. I suppose it's possible that baking soda might have a small effect over time on Ph, but to see it change that fast surprises me. See the site and quote below:

From the site: http://www.drhelm.com/aquarium/chemistry.html

Ways to increase kH:

· Adding sodium bicarbonate (baking soda). One teaspoon of baking soda added to 50 liters of water can raise the kH of the water by approx 4 OdH without a major affect on pH.
· Adding an air stone to increase surface turbulence driving off carbon dioxide (CO2)
· Adding commercially available products to increase buffering capacity

Ways to lower kH


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## Milan (Jul 6, 2005)

imatrout said:


> Adding sodium bicarbonate (baking soda). One teaspoon of baking soda added to 50 liters of water can raise the kH of the water by approx 4 OdH without a major affect on pH.


I think the key word in this statement is "major". What's major or minor, that's a different story, but here is the link to calculate the affect of baking soda on KH and pH.


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## dennis (Mar 1, 2004)

imatrout....
yes I believe the key word there is major. I don't remember the exact numbers but raising my kH by 2 degrees increased my ph from something like 6.3 to 6.5. If you look at a CO2 chart you can pretty much figure your increase in kH will proportionally rais ethe pH the same amout, due to the fact that your CO2 concentration will stay the same

also, you quoted...



> Ways to increase kH:
> 
> · Adding sodium bicarbonate (baking soda). One teaspoon of baking soda added to 50 liters of water can raise the kH of the water by approx 4 OdH without a major affect on pH.
> · Adding an air stone to increase surface turbulence driving off carbon dioxide (CO2)
> · Adding commercially available products to increase buffering capacity


 The first point is right, as is the third. However, the second point is incorrect. Driving off CO2 would increase the pH however the kH would remain unaffected. CO2, when it combines with water, forms cabonic acid, hence the reason your pH drop with CO2 addition.

Adjusting your kh will have no affect on CO2 concentrations in your water. Your water will hold what it holds but I can assure you it will hold 30ppm regardless of the kh or ph. Your CO2 production is what needs improvment, not your water.


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## dennis (Mar 1, 2004)

Milan,

I checked that link at it does make sense. However, I don't think the pH increase calculation takes into account the effects of Co2 addition. I know my pH only rose .2-.3 by raising the kh 1-2 degrees. The link gives me a pH increase of.7 for a kH increase of 2


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