CO2 production at night

stephanieleah

i was just considering how plants produce CO2 at night...does this happen when the lights go off? i wonder how this is triggered?

but what i really wondered is whether it would be helpful to decrease the night period to a minimum of say 8-10 hours in order to limit the amount of CO2 for the fish? or would having a night period of 10-12 hours be better so that the CO2 balance is better for the plants? are the amounts so minute that it doesn't even make a difference?

Claudia1002

They produce CO2 the same as we do by respiration. :)

Plants are always consuming oxygen with the lights on or off. It is done through their root cells which do not carry out photosynthesis. They produce much more O2 during the day than they consume at night.

Photosynthesis is used to make glucose which is stored. The root cells will use the glucose plus oxygen to make energy. It's one of the reasons you can't let sand compact around the roots or else you'll asphyxiate them.

Angel079

Very good post right there by Claudia!
I would like to add that shorting the night phase; in other words lengthening the day time (lights on longer) wouldn't be beneficial. Ideally you want to come as close to nature in your tank as you can naturally you'd see some 8hrs full daylight plus sunrise & sunset so you're looking at a max of 10hrs tank lights on.

Byron

Claudia is correct. Plants and fish both produce CO2 continually and assimilate oxygen continually, day or night there is no change.

Plants consume CO2 during photosynthesis (only occurs in daylight) and produce oxygen, some of which travels down to the roots to be released for bacteria to use in the substrate. And as was said, more oxygen is produced than the plants can use, so it benefits the fish and bacteria.

During darkness the plants rest, and this is crucial, just as it is for fish and all animals, and for exactly the same reasons. Hiscock mentions 10 hours of absolute darkness, and I've not read anyone suggesting differently. I have a lot of fish and plants in my aquaria, and they have 10+ hours of darkness, and I have never noticed the slightest sign of respiration issues that would suggest a deficiency of oxygen in the very early morning. Also bear in mind that during periods of total inactivity (night) much less oxygen is required and correspondingly less CO2 is released than during high activity.

In high-tech aquaria with CO2 diffusion, most recommend turning it off at night to avoid overloading the system and poisoning the fish, and some further recommend turning on an aerator at night; this is because the CO2 diffusion is pumping considerably more CO2 in the aquarium than the plants can probably use (they are very slow at assimilating CO2 as I detail in one of the stickies) and it is more likely to create an imbalance that could be detrimental. But I do not personally believe this is likely in a natural (low-tech) system.

An indication of this is the pH fluctuation that naturally occurs every 24 hours in planted aquaria as it does in nature. During the day, as CO2 is consumed, the pH rises; during night when CO2 is being replenished, the pH drops back. In my aquaria the fluctuation is about 3 or 4 decimal points, say from 6.2 at dawn to 6.5 at dusk. This is not a concern.

Byron.

stephanieleah

Thanks guys, this has been helpful. I actually think I need to adjust my timers. And again, despite the repetition of information that I know I've read posted here, it's always so very useful to read it again (obviously, as I hadn't understood how to apply it to my question!)

Claudia1002

My CO2 runs day and night to avoid pH fluctuations and my lights are on 10 hours a day. I've got fairly hard water so I don't get the pH crash some people with soft water would, but I can tell you that my fish have been happier for leaving it on.
With running CO2 at 25-30 ppm all day and night, the fish have never shown signs of a problem. I look to my cardinals for telling me if there is a problem, and they've been just fine.


As far as what plants do at night, I guess it depends on the species.
My Water Sprite is quite the busy body at night. The plant won't change at all during the day. The next morning, I'll wake up to Water Sprite that has stretched up and out. It's the fastest growing plant I have and runs circles around the other plants is the only reason I've noticed. I'll have to pay closer attention to some of the others to see if they're the same way.

stephanieleah

Claudia, I have really enjoyed reading your posts, in this thread and others. Thank you for you input and insights.