Turning off CO2 at night

[PaulS]

This is advice I recieved from a very experienced aquatic plant person about turning off C02 at night. He certainly makes a good case for leaving the CO2 running 24/7. I thought it was very interesting and I'd like to know what other members of this group do.

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You'll find that erogating CO2 24/7 produces the best results and stability in PH. Turning CO2 off at night can cause some large swings in PH which most plant people will advise you against.

The "CO2 off at night" thing is unfortunately one of those myths we just can't seem to shake off. There are some scenarios where this is advisable but in most cases maintaining good CO2 levels is a balancing act between gas exchanges (CO2 loss) and bubble rate (CO2 additions), neither of these components change during the night period. Plant activity plays a very minor role in CO2 levels as their uptake rate is very small compared to what is lost to gas exchanges. Therefore even though plants stop using CO2 at night, and actually emit a little back into the environment, it has a very small impact overall on levels.

You have to consider that at least 90% of the CO2 we put into the tank is lost through gas exchanges, less than 10% is actually consumed by the plants. So CO2 and PH levels are minimally effected by the plants' activities. It is just another of those myths that is born from a pinch of theory... in practice it's a whole different story. Another common myth is that CO2 displaces O2...

You'll also find that it can take hours for the tank's CO2 levels to reach the desired level once the system turns on with the lights, this can cause a further delay for the plants who already have a rather long ramp-up time as is. Solenoids are great for those using a PH controller.
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[Aaron]

I've had success doing it either way. If I do 24/7 I use a slower bubble count. Either way the fish were fat and happy.

[Ben Belton]

I don't know that I agree with all of it, but I have done both, and I can't tell the difference. My CO2 is off at night. It's on a timer. So it's not like it takes effort and it saves CO2 which can be a pain to go get sometimes when I'm busy. I "feel" better/safer with it off at night. So there is 2 reasons in the "off at night" column and no reasons in the "on 24 hours" column.

[Ghazanfar Ghori]

Plant activity plays a very minor role in CO2 levels as their uptake rate is very small compared to what is lost to gas exchanges

On a stem plant tank, w/ CO2 running 24/7 - measure the CO2 in the morning
before lights on and then again after about 4 hours. The difference can be big.
I've seen it go from 30ppm to 12ppm within a period of 3-4 hours. Thats how
much plants can take up - so the pH does swing a bit during the day. How much,
depends on your KH / buffering.

That said - I'm sure that a significant portion of what we're putting in get outgassed and like Aaron - I've had success both ways but for a 24/7 I'd use
a slower bubble count.

[jcali10]

I'm no biologist, but I see no reason to run CO2 at night unless maybe you don't have a solenoid. I realize in nature you can't shut off the CO2 produced in a lake or river bed. But I can and do. I believe, at night when photosynthesis is not occuring, the plants take in O2 and respire CO2.

True pH would fluctuate some. CO2 is a major factor in plant growth and is usually a limiting factor.

By shutting it off at night, there's less chance of building up a toxic level of CO2 in your glass box.

[JMLenke]

Currently, I have the Co2 running into a bubbler behind a screen prefilter for a powerhead that shuts off when the lights go out.

I am STILL waiting for my order from Aqua magic but until then I have a "guess" at my Co2 levels.

The fish arent gasping and the plants are growing.

[krisw]

I've done it both ways, and have seen little difference besides the frequency that I need to go and refill my CO2 tanks. For that reason alone, I turn them off at night, and only visit the "gas store" once every 6-12 months.

[eleontie]

Yeast and sugar CO2 runs out anyways once every two weeks. And it would be a headache to turn off.
So ... I let it flow.


It seems that there are other reasons than science to turn it off at night.

Eugen

[krisw]

Yes, if you're usually yeast, definitely do not shut it off -- your bottle could explode due to the pressure -- big mess!

[RTRJR]

I don't think the tank effect on pH is very meaningful to the fish under any circumstances - they don't read it anyway.

If you do shut off during the dark cycle, it should be back on before the lights, not co-timed, to have the CO2 back up when photosythesis starts.

You can shut off DIY fermentations at night if you wish. A plastic air valve spliced it to vent to the air works, but that is full manual on/off operation. Automation would be overkill there. I don't see the point though, DIY is not generally going to give you a log depression of the pH unless you spend a lot on money of sugar.