# Confusion over maintaining proper pH levels when injecting CO2.



## asincero (Mar 25, 2006)

I've noticed that when I add CO2 to the tank, the pH drops. Doing some research, I discovered that when adding CO2 to the tank, carbonic acid forms. So a drop in pH makes sense since the water is becoming more aciditic. However, this strikes me as being a bad thing since my fish need alkaline water (pH of at least 7.6).

How can I inject CO2 for my plants while still making my alkaline water-loving fish happy? The injection system I'm using is a DIY system utilizing a yeast and sugar concoction to make the CO2 and a Hagen ladder to diffuse it. Perhaps I'm injecting too much CO2?

Should I be using products like pH-UP to raise the pH to the desired levels when utilizing CO2 injection?


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## BryceM (Nov 6, 2005)

NO! Do not use pH adjusting products. They are a poor (and temporary) fix that will cause more problems than almost anything else you can do to a planted tank.

We have often used pH to describe the type of water that fish prefer, when in reality, it would be more correct to describe the quantity of dissolved solids (Calcium and Magnesium which account for General Hardness - and carbonates which account for most of the buffering capacity or KH). In the absence of CO2, water with high KH tends to have a high pH and water with a low KH tends to be acidic.

Fish tend to tollerate the pH changes caused by the addition of CO2 very well (as long as it's within reason and changes are made slowly). My tank is at pH 6.3 right now and the fish (mostly tetras) are perfectly happy. If you are keeping african chiclids you'll want it higher, but don't worry too much about the pH depression caused by CO2.


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## billionzz (Apr 9, 2005)

I have kept african chiclids at a pH of 6.8 and they did well. They kept their color and breed, no problems at all.

Bill


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## Salt (Apr 5, 2005)

Go by what the pH is _without_ CO2 being injected to the tank to gauge if it's proper for the species of fish you are keeping.

CO2 is thought of as a "fake" pH drop. Many people (including me) use pressurized CO2 and have it switch off at night. The resulting massive pH swings have little to no effect on the fauna.


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## Salt (Apr 5, 2005)

guaiac_boy said:


> Fish tend to tollerate the pH changes caused by the addition of CO2 very well (as long as it's within reason and changes are made slowly).


My pH with pressurized CO2 being injected = 6.7
My pH with pressurized CO2 switched off every night = 7.4
My current kH = 87 ppm as CaCO3
Time it takes pH to change = about 2 hours
Effect on tank fauna = none


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## BryceM (Nov 6, 2005)

Salt said:


> My pH with pressurized CO2 being injected = 6.7
> My pH with pressurized CO2 switched off every night = 7.4
> My current kH = 87 ppm as CaCO3
> Time it takes pH to change = about 2 hours
> Effect on tank fauna = none


I'm suggesting that it's a bad idea to try going from pH 8.6 to pH 5.5 in a single day. You need to be reasonable. A pH drop of 0.7 units isn't too huge, but cranking up the CO2 and leaving town for a couple of days is a bad idea. At some point the fish will start showing signs of stress. It's best to approach this slowly, to be able to recognize it and turn the CO2 down a bit.


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## asincero (Mar 25, 2006)

I've been looking into putting together an automatic pressurized CO2 system that's controlled by a pH monitor. I don't have any real world experience with these systems and the only thing I know about them is what I've been reading so far off the 'net. Since my fish want a pH of around 7.6, I'm hoping that I could just set on the pH monitor "don't let the pH fall below 7.6" and let the thing control the CO2 output for me.

Here's where I'm confused. Say that I want CO2 levels to be at 25ppm. The water without CO2 has a pH of 7.6. If I set on the pH monitor "don't let the pH fall below 7.6" and the pH is already 7.6, then that means the pH monitor won't ever turn the CO2 on. Unless, I can calculate how much 25ppm of CO2 will lower the pH by and set the pH monitor to that.

However, I have been reading up on KH and it's relationship to pH. Unless I'm even more confused than I thought, the higher the alkalinity, the more acid you need to add to the water to cause the pH to drop. Or in other words, the higher the alkalinity the more stable the pH will be. So, if I want to put in the pH monitor "don't let the pH fall below 7.6" and I want to have CO2 levels at 25ppm, I need to figure out what degree I need to get the KH to in order to maintain these levels. Right?


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## BryceM (Nov 6, 2005)

You can't manipulate CO2 levels by changing KH. You only set the "starting point." If you have fish that "want to be" at pH 7.6, you'd ideally want the KH to be at 6 or 7. Then, add CO2 until the new pH is 6.6. A 1 pH unit drop will put you in an ideal spot for keeping healthy plants, somewhere around 30 ppm. The fish will generally not be bothered by this amount of CO2 addition at all. If you use a controller you'll need to make sure that the KH is fairly stable.


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## asincero (Mar 25, 2006)

guaiac_boy said:


> You can't manipulate CO2 levels by changing KH. You only set the "starting point." If you have fish that "want to be" at pH 7.6, you'd ideally want the KH to be at 6 or 7. Then, add CO2 until the new pH is 6.6. A 1 pH unit drop will put you in an ideal spot for keeping healthy plants, somewhere around 30 ppm. The fish will generally not be bothered by this amount of CO2 addition at all. If you use a controller you'll need to make sure that the KH is fairly stable.


Well, I didn't mean to imply that you can manipulate CO2 levels by changing KH. I was theorizing that if I raise KH, the carbonic acid being produced by injecting CO2 won't lower the pH. That is, unless I was putting in too much CO2 (i.e. maxing out the buffering capacity of the carbonates). Then, the pH will start to drop. Right?

However, I was playing around with the CO2 calculator at:

http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

And I guess if my KH is 6 degrees, I should set the pH monitor to "don't let my pH fall below 6.9", and it'll pump enough CO2 to give me about 22ppm. Since you guys are saying "ignore the pH drop caused by CO2 injection", I guess this would be ok, eh?


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## BryceM (Nov 6, 2005)

No, no matter what your KH is, _any_ addition of CO2 will lower pH.

I would set your pH controller to keep the pH at 1.0 units below your baseline pH. If your baseline pH (after letting the water come to equilibrium with the atmosphere for 24 or 48 hours) is 7.6, then set your controller to 6.6, etc.


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## asincero (Mar 25, 2006)

guaiac_boy said:


> No, no matter what your KH is, _any_ addition of CO2 will lower pH.
> 
> I would set your pH controller to keep the pH at 1.0 units below your baseline pH. If your baseline pH (after letting the water come to equilibrium with the atmosphere for 24 or 48 hours) is 7.6, then set your controller to 6.6, etc.


Ahh .. I see. I didn't know that any addition of CO2 to the water will lower the pH.

Anyway, thanks for advice. That last paragraph up there is basically what I needed to know.


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## BryceM (Nov 6, 2005)

Cool. good luck, and remember to check your KH occasionally. If it changes, the controller will then be "set" incorrectly, since the baseline pH will be different.


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