CO2 pH swings? Need opinions/advice - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 10-27-2014, 06:47 PM Thread Starter
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CO2 pH swings? Need opinions/advice

What's up guys?

I want to start dosing co2 in aquarium , but im a little scared of throwing my pH out of balance and killing my fish.

I know every tank is different , but can I have your opinion on how much my pH can drop? Or if I will be okay?

Here are my parameters.

Ammonia : 0
Nitrite:0
Nitrate: 0
PH: 8.0
KH: 8 degrees

I have not tested my GH yet, sorry.

I know some parameters are a bit high, but my live stock doesn't mind and my plants have been doing well. I would prefer not to add any pH or KH adjusters.

So to stick to the point, will DIY co2 cause significant pH swings based on my parameters ? Will my fish mind ? Will it kill them?


Thanks
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post #2 of 8 (permalink) Old 10-27-2014, 06:55 PM
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your carbonate buffer is quite high, IMO CO2 will not have any impact on your pH
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post #3 of 8 (permalink) Old 10-27-2014, 06:57 PM
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The pH swing won't matter.. KH swings are what really kill fish in most "pH" problems, but CO2 doesn't change the KH.

That said, you can easily kill your fish by suffocating them with high CO2 concentrations.... Worry more about that than the pH change.


https://www.plantedtank.net/forums/sh...d.php?t=158325

In particular read post 5 by Hoppy...

Quote:
Fish don't generally have pH requirements. Some do have requirements for low or high KH, but not pH.
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post #4 of 8 (permalink) Old 10-27-2014, 07:10 PM Thread Starter
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Thank you !
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post #5 of 8 (permalink) Old 10-27-2014, 08:33 PM
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Hi,

If this is, a religious matter read no further.

Many fish have rather specific water chemistry requirements including KH (more generally Alkalinity), GH and pH.

Assuming you have no highly specialized critters, adding CO2 should not be a problem. The addition of CO2 will change the pH if the system Alkalinity is principally KH. A full pH drop represents the addition of about 27-ppm CO2 (25C (77F), 1-atm), about 30-ppm in the tank, which as luck would have it is just about the amount of solvated CO2 required to saturate the Prantl boundary (yea, us).

{A correction is in red above, I had said "Each full," Hoppy the kindly Guru he is pointed out the error of my way, thank you, Hoppy}

Changing pH by the addition of CO2 is an exception to the pH drop rule. Generally changes greater than about pH 0.25 per day are hazardous.

This is why you hear some say things as “pH drops do not affect critters, it is KH drops.” The bit of truth is that pH is purely notational, so someone dumping sulfuric acid in the tank would be correct in saying the sudden pH change didn’t cause the deaths, it was the consumption of the buffer.

A danger in our highly stocked tanks is reducing the CO2, since the effect of pH on the ammonium/ammonia ratio does not care why the pH rises or falls.

Respectfully,
Joe
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Last edited by JoeRoun; 10-28-2014 at 07:19 AM. Reason: correction in red, thanks Hoppy
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post #6 of 8 (permalink) Old 10-28-2014, 04:14 AM
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Quote:
Originally Posted by JoeRoun View Post
Hi,

Each full pH drop represents the addition of about 27-ppm CO2 (25C (77F), 1-atm), about 30-ppm in the tank, which as luck would have it is just about the amount of solvated CO2 required to saturate the Prantl boundary (yea, us).


Respectfully,
Joe
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A drop in pH by 1.0 represents a 10X increase in ppm of CO2. If you start with 2.7 ppm of CO2, then the 1.0 drop means you have 27 ppm. But, 2.0 drop in pH means a 100X increase in ppm of CO2, so that second 1.0 drop in pH means you have 270 ppm of CO2 in the water. (In reality I doubt that you could get 270 ppm to dissolve in the water, and if the pH started at less than about 7 you couldn't get the pH to drop by 2.0.)

This is a religious matter

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post #7 of 8 (permalink) Old 10-28-2014, 07:14 AM
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Quote:
Originally Posted by Hoppy View Post
A drop in pH by 1.0 represents a 10X increase in ppm of CO2. If you start with 2.7 ppm of CO2, then the 1.0 drop means you have 27 ppm. But, 2.0 drop in pH means a 100X increase in ppm of CO2, so that second 1.0 drop in pH means you have 270 ppm of CO2 in the water. (In reality I doubt that you could get 270 ppm to dissolve in the water, and if the pH started at less than about 7 you couldn't get the pH to drop by 2.0.)

This is a religious matter
Hi Hoppy,

Thank you for the correction, probably why we recommend a pH 1 drop. I will correct the above entry, crediting you that none should be led astray from the true path of aquatic plant enlightenment.


For the record my somewhat out of date religious book(*) tells me we if we do everything just right at 25C (77F) and 1-atm we can get 1450-ppm CO2. My practical experience is that at 25C and 0.955-atm I get about 1275-ppm. I use carbonated water so we end up figuring 1.28-miligrams CO2 per milliliter.

Respectfully,
Joe
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(*)CRC Handbook of Chemistry and Physics, 86th Edition

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Last edited by JoeRoun; 10-28-2014 at 07:22 AM. Reason: Font
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post #8 of 8 (permalink) Old 10-28-2014, 04:31 PM
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The reason I doubt that we can get 270 ppm of CO2 in our aquarium water is the difficulty of supplying it faster than it outgases from the water surface. If we seal off the air chamber above the water, so the concentration of CO2 in that air can also rise, then it shouldn't be hard to get that much to dissolve in the aquarium. But, of course we don't do that. (And, much less than 270 ppm of CO2 would kill off all of the fish anyway.)

Speaking of the CRC Handbook of Chemistry and Physics, I tried to sell my copy on Craigslist and Ebay and had no takers! People just don't recognize what a great book it is! The plot drags, but it still holds your attention.

Hoppy
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