CO2 and pH fluctuating.........

PeaP

Hello.
Can someone help me with co2 and pH...I have CO2 injection and I turn it off at night so I want to know if this can harm fish because of fluctuating pH.
Greetings and thank you for advices
 

GlennO

It's normal practice to shut down CO2 injection when lights are off. The fluctuating pH between when CO2 is on and off does not seem to bother my fish nor do I hear of it being an issue for others. The pH changes gradually over several hours.
 

PeaP

It's normal practice to shut down CO2 injection when lights are off. The fluctuating pH between when CO2 is on and off does not seem to bother my fish nor do I hear of it being an issue for others. The pH changes gradually over several hours.
Ok thanks
 

SparkyJones

Yeah from what I know about it, GlennO is correct. Maybe check your KH make sure you have KH, so you have buffer for carbonic acid but there should be some pH rise and fall with it on and off.

that's the only thing I could see becoming a problem for it, if you ran out KH somehow, like by not water changing or something.

There is a fixed relationship between the pH, KH, and CO2 level. As you increase the amount of CO2 that is dissolved into the water, the pH will drop. And if you then stop adding CO2, the pH will climb as that extra CO2 is released from the water.
Generally, in simple terms with the light off the plants are using oxygen and producing CO2, and with the light on using CO2 and producing Oxygen.
The KH will move the start and end pH values, but that pH swing will be the same for the ppm CO2 setting you have it at. A higher KH might make a smaller swing, but a lower KH doesn't make a bigger swing. increasing CO2 ppm can cause a bigger swing.

Disclaimer: what I know about aquatic plants and this subject is just from books, I have no working knowledge of it in practice.

The drastic (big pH drop in a short period of time) is usually a combination of things between CO2 releasing with the lights off, near no KH to buffer the carbonic acid, and small water volume and sometimes O2 being pushed out and consumed by the plants with the light off and replaced by CO2 that causes the fish distress, and not quite the pH drop that was the issue that shocked the fish.
That can happen anyways without CO2 injection in a low tech tank though so it still wouldn't be the CO2 injection doing it I don't think.
In a low tech planted tank there is also a pH rise and fall between night and day time and how the plants are respiring or photosynthesizing. using O2 and producing CO2 or Using CO2 and producing O2.
 

PeaP

Yeah from what I know about it, GlennO is correct. Maybe check your KH make sure you have KH, so you have buffer for carbonic acid but there should be some pH rise and fall with it on and off.

that's the only thing I could see becoming a problem for it, if you ran out KH somehow, like by not water changing or something.

There is a fixed relationship between the pH, KH, and CO2 level. As you increase the amount of CO2 that is dissolved into the water, the pH will drop. And if you then stop adding CO2, the pH will climb as that extra CO2 is released from the water.
Generally, in simple terms with the light off the plants are using oxygen and producing CO2, and with the light on using CO2 and producing Oxygen.
The KH will move the start and end pH values, but that pH swing will be the same for the ppm CO2 setting you have it at. A higher KH might make a smaller swing, but a lower KH doesn't make a bigger swing. increasing CO2 ppm can cause a bigger swing.

Disclaimer: what I know about aquatic plants and this subject is just from books, I have no working knowledge of it in practice.

The drastic (big pH drop in a short period of time) is usually a combination of things between CO2 releasing with the lights off, near no KH to buffer the carbonic acid, and small water volume and sometimes O2 being pushed out and consumed by the plants with the light off and replaced by CO2 that causes the fish distress, and not quite the pH drop that was the issue that shocked the fish.
That can happen anyways without CO2 injection in a low tech tank though so it still wouldn't be the CO2 injection doing it I don't think.
In a low tech planted tank there is also a pH rise and fall between night and day time and how the plants are respiring or photosynthesizing. using O2 and producing CO2 or Using CO2 and producing O2.
Thankyou for this very detailed explanation:)
 

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