Do changes in pH due to CO2 affect fish?
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Old 01-20-2013, 11:56 PM   #1
souffle
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Do changes in pH due to CO2 affect fish?


Hi planted tankers,

I've read on this forum that pH swings due to CO2 changes are not harmful to fish (I'm looking into whether I should be turning off CO2 at night)

On the other hand, I've also read that adding CO2 to a tank is a good way to make conditions better for fish requiring low pH.

Surely these can't both be right? Anyone know which one is correct?

Thanks for your help!
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Old 01-21-2013, 12:06 AM   #2
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pH swings, no matter what they are caused by, are not good for fish. It can stress them or even kill them.
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Old 01-21-2013, 12:14 AM   #3
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Quote:
I've read on this forum that pH swings due to CO2 changes are not harmful to fish
I've heard this off and on for some time. Never really trusted that theory though, just seems to me a PH swing be it because of adding something that changes it like wood or peat moss, would be the same as a PH changed because of CO2. Subbing this so I see some other opinions on this.
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Old 01-21-2013, 11:28 PM   #4
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Quote:
Originally Posted by Sake View Post
I've heard this off and on for some time. Never really trusted that theory though, just seems to me a PH swing be it because of adding something that changes it like wood or peat moss, would be the same as a PH changed because of CO2. Subbing this so I see some other opinions on this.
Yeah it sounded suspect to me too... but i then I read it on a post by Tom Barre, who usually seems to know all
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Old 01-21-2013, 11:31 PM   #5
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In short: no, CO2-related pH changes won't hurt your fish. Hardness (KH & GH) remain the same and it is way more important than pH. It's the carbonic acid that causes the pH "swing" in your tank.

If you use the search feature here on the forum, you'll find dozens of threads that go extremely in-depth on the matter.
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Old 01-22-2013, 07:13 AM   #6
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Ok thanks for that somewhatshocked. Have done some reading and think I get it(more or less):

PH can change by two different pathways, via changes to levels of carbonic acid (caused by co2 injection) or via changes to levels of carbonate (caused by changing kh). Changes to the former pathway don't affect fish, but changes to the latter do. So we should avoid rapid swings in ph if they're caused by rapid changes in kh, but not worry about them if they're caused by changing levels of co2.

Sound right?
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Old 01-22-2013, 01:18 PM   #7
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Sounds about right to me.
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Old 01-22-2013, 02:21 PM   #8
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souffle (imo) you have it based on your last post.
Having the equipment here I've placed electronic pH controllers on low light NPT systems just to see what happens during a 24hr period. Lighting alone can shift tested pH by a full degree. Monitoring what the pH reading was in the morning before the photoperiod and again late in the afternoon I recorded a full point shift in value. The only difference was lights on or lights off (more or less CO2). Rapid shifts (swings) in GH, KH, TDS, (changes in osmotic pressure) that's what causes our critters issues not pH changes per say.
pH value is a product of carbonate buffers and CO2 content in the water for this conversation. Acidic or alkaline yes but testing pH as it relates to tank water and your question I agree with the answer you received, it really isn't anything to worry about.

As long as the temperature is matched I routinely swap fish between injected tanks with 5.9/6.2pH and 7.4/7.6pH low techs.
Temps the same, the TDS is very close and fish don't seem to care is why I support the position that CO2 induced swings don't matter.

When people say a fish requires a low pH I automatically read that as soft water.
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Old 01-23-2013, 12:14 AM   #9
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PH can change by two different pathways, via changes to levels of carbonic acid (caused by co2 injection) or via changes to levels of carbonate (caused by changing kh). Changes to the former pathway don't affect fish, but changes to the latter do. So we should avoid rapid swings in ph if they're caused by rapid changes in kh, but not worry about them if they're caused by changing levels of co2.

This actually makes sense because I always thought that pH swings were stressful toward fish too. My tank is also CO2 and it was also a fear of mine. This makes sense for those who run CO2 on timers vs pH controllers, the pH swings won't affect the fish because the chemical makeup of water itself isn't changed. This was a very good post!




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Old 01-23-2013, 12:15 AM   #10
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Quote:
Originally Posted by mohican
PH can change by two different pathways, via changes to levels of carbonic acid (caused by co2 injection) or via changes to levels of carbonate (caused by changing kh). Changes to the former pathway don't affect fish, but changes to the latter do. So we should avoid rapid swings in ph if they're caused by rapid changes in kh, but not worry about them if they're caused by changing levels of co2.
--end quote--

This actually makes sense because I always thought that pH swings were stressful toward fish too. My tank is also CO2 and it was also a fear of mine. This makes sense for those who run CO2 on timers vs pH controllers, the pH swings won't affect the fish because the chemical makeup of water itself isn't changed. This was a very good post!




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