CO2 at night?

[Ryehard]

From what I've read it seems that you want to shut your CO2 off when the lights go out since the plants aren't using it and are in fact releasing CO2, but will the PH spike hurt more than a CO2 spike? Mine goes from just under a neutral PH to just over 8.0 by morning...

 

[ringfinger]

So yours goes from 6.9 to 8.0 overnight? That is quite the increase...

You might consider getting a pH controller if you're jumping around that much.

 

[malkore]

that's a huge swing.

i run CO2 24/7 on all 3 planted tanks. i have a natural pH of 7.8 with 9-10dKh.

a pH controller will let you use less CO2 by shutting it off occasionally, but still maintaining a steady pH and CO2 level.

 

[Wizzard~Of~Ozz]

AFAIK, Plants don't release Co2, ever.. they consume Co2 even at night to create glucose I believe.. (read about dark reaction and light reaction)

The only thing that comes to mind with a huge swing like that is a very low KH, a PH controller is a good idea to keep the Co2 level constant as plants still consume Co2 at night, just not at the same rate..

a good read on how plants work is Here

 

[Ryehard]

I probably read that somewhere on a website about releasing CO2 as a respiration byproduct in the absence of light, but I can't remember where so who knows how good the source was . My water out of the tap is a ph of 8.2 and kh of 6 (ran through my faucet filter), so I'm guessing when the CO2 is shut off then it wants to go back to what it's buffered to without excess CO2? Should I keep the CO2 on 24/7 then and see how the ph is in the morning before I turn on the light?

 

[7Enigma]

Ryehard,

Yes I would try with the CO2 on all the time and check the pH in the morning. Since your KH is moderate/high it will most likely be better than shutting off at night and turning on in the morning.

Wizzard~Of~Ozz,

The light cycle only occurs in the presence of light, but (and this is confusing due to the name) the Dark cycle is going on ALL THE TIME (when the proper components are available). Both during the day and at night plants do indeed produce CO2 (and uptake O2). They respire in the same way that we do, they uptake the stored glucose in their roots and use oxygen to breakdown and use the energy for growth. It's just that due to the lack of light the other components required to fix CO2 are not available and the Dark cycle slows/stalls. When this happens the plant begins to PRODUCE more CO2 than it uses and you have a net INCREASE of CO2. This is a real concern for us that have DIY since we generally don't use pH controllers and run 24hr systems.

So basically, plants are using BOTH CO2 and O2 during much of the day/night, but its the RATIO of use that concerns us. During the day they are primarily using CO2 and releasing O2, and during the night they are primarily using O2 and releasing CO2. This is why closed systems with plants are able to work for long periods of time as long as nutrients and light are present (remember making a plant in gradeschool where you put it inside a 2L soda bottle and completely closed it off? This is only possible since the plant jumps back and forth between using and releasing O2. True the growth will be stunted in these plants because they will have a finite amount of carbon (will get some from the soil), but they will survive, whereas humans obviously would suffocate rather quickly).


The way I attempt to overcome this large fluctuation is that during the day my HOB aquaclear filter is on the lowest flow (so the least amount of CO2 can escape, as well as the least amount of fish food is sucked up), and at night the flow is switched to maximum (so that the CO2 can be gassed out most efficiently and a greater amount of O2 can be introduced to the water since the plants will be using and NOT producing O2, as well as a higher level of filtration).

This has helped to reduce the stress on the fish from oxygen deprivation and pH swings.

 

[Glenc]

I leave my CO2 on 24/7. I'm at a steady 25 to 30 ppm CO2. My ph is 8 without CO2 and 6.9 to 7 with it. I let it run to avoid the ph swing that would occur if I shut it down at night. I know cause I have shut it off at night, ph went back up to 8, fish were not happy. I've seen no I'll effects on plants or fish by running CO2 all the time. I like 7Enigma's suggestion on adjusting the flow on your HOB. Makes sense. Gonna give it a try and see what happens.

 

[Ryehard]

Yeah that sounds like a good idea, I hadn't thought of controlling CO2 levels by how quickly they're outgassed. I run my aquaclear on the lowest setting during the day as well, so I'll try turning up the current at night. As it is, I left the CO2 on and this morning the PH was 6.8 (possibly slightly less, I'm horrible at reading the colors). That would mean my CO2 got up to in the mid 30's max which is high but alright? Otherwise going from 7 - 6.8 seems better than 7 - 8 ph and my gourami looks much more colorful and happy. Hopefully I'll get even better results with the agitation turned up. Thanks guys!

 

[Wizzard~Of~Ozz]

Wizzard~Of~Ozz,

The light cycle only occurs in the presence of light, but (and this is confusing due to the name) the Dark cycle is going on ALL THE TIME (when the proper components are available). Both during the day and at night plants do indeed produce CO2 (and uptake O2). They respire in the same way that we do, they uptake the stored glucose in their roots and use oxygen to breakdown and use the energy for growth. It's just that due to the lack of light the other components required to fix CO2 are not available and the Dark cycle slows/stalls. When this happens the plant begins to PRODUCE more CO2 than it uses and you have a net INCREASE of CO2. This is a real concern for us that have DIY since we generally don't use pH controllers and run 24hr systems.

So basically, plants are using BOTH CO2 and O2 during much of the day/night, but its the RATIO of use that concerns us. During the day they are primarily using CO2 and releasing O2, and during the night they are primarily using O2 and releasing CO2. This is why closed systems with plants are able to work for long periods of time as long as nutrients and light are present (remember making a plant in gradeschool where you put it inside a 2L soda bottle and completely closed it off? This is only possible since the plant jumps back and forth between using and releasing O2. True the growth will be stunted in these plants because they will have a finite amount of carbon (will get some from the soil), but they will survive, whereas humans obviously would suffocate rather quickly).


The way I attempt to overcome this large fluctuation is that during the day my HOB aquaclear filter is on the lowest flow (so the least amount of CO2 can escape, as well as the least amount of fish food is sucked up), and at night the flow is switched to maximum (so that the CO2 can be gassed out most efficiently and a greater amount of O2 can be introduced to the water since the plants will be using and NOT producing O2, as well as a higher level of filtration).

This has helped to reduce the stress on the fish from oxygen deprivation and pH swings.

Glucose requires 6 Co2 and 6 H2O molecules, nowhere have I read that they consume O2 at all, infact plants should continue to produce O2 well into the night during the dark cycle (yes i know that term is misleading since it does operate during the light mainly)

The dark reaction takes place in the stroma within the chloroplast, and converts CO2 to sugar. This reaction doesn't directly need light in order to occur, but it does need the products of the light reaction (ATP and another chemical called NADPH). The dark reaction involves a cycle called the Calvin cycle in which CO2 and energy from ATP are used to form sugar

Using 6 Co2 molecules and 6 H2O molecules results in C6H12O6(glucose) + 6O2 (6 O2 molecules) so it is the dark reaction that produces the oxygen, this would be produced all through the night just at lower levels since the energy it is using is stored and not being created rapidly. (more light, more O2, more growth since energy can be converted faster by photosynthesis.)

I must note, I'm talking strictly of the photosynthetic portion, I'm still reading the conversion of sugars to starches and such..

Well, what I've read thus far, you are correct.. respiration does take place to use the stored energy, it consumes oxygen to create Co2 to use the stored energy, but in the same token, the dark reaction will consume the Co2.. so it's a question of balance, if the 2 are equal then they would negate themselves thus leaving the Co2 level unchanged over night.

Glad I didn't take biology.. but it is some good reading.

Carbon dioxide(CO2) is a raw material required for photosynthesis.
The atmospheric CO2 concentration at the plant level is the most important
rate determining factor for further increases in photosynthesis and yield
(18). CO2 concentrations may fall below the ambient air concentration
.03% (300 ppm) in the greenhouse when weather conditions restrict ventilation
or infiltration. A crop in a tightly closed greenhouse will soon deplete
the CO2 concentration which reduces growth and production by slowing or
stopping photosynthesis. Unless replaced, the CO2 concentration will remain
at the plants compensation point, the level at which the CO2 produced
from respiration equals the amount used for photosynthesis. No growth
occurs at this point.

So in the end, if the plant is growing then it's consuming more Co2 then it produces, even in darkness, thus your Co2 level should be lower in the morning then it was that night if your Co2 is turned off.

 

[7Enigma]

"...so it's a question of balance, if the 2 are equal then they would negate themselves thus leaving the Co2 level unchanged over night."

But we know for a fact that the 2 are not equal during dark hours. This is easily tested by taking the pH of the water right before the lights go out, during the middle of the night, and again right before the lights come on. You will see a steady decrease in the pH. This can only come from the increased concentration of CO2 in the water.

There are then 2 possibilities for why/how this happened:

1. The plants cannot use as much CO2 due to the lack of light, so the CO2 rises in the tank since the DIY/pressurized CO2 does not vary in production during the day/night (within reason due to temp changes in the room).

2. The plants are actively using O2 and releasing CO2 as they are breaking down the stored energy. This CO2 is entering the water and increasing the CO2 concentration and lowers the pH.

I think its important to note that in our tanks #1 is primarily responsible for the pH drop that occurs at night, but #2 only increases this pH drop. Either way, it doesn't really matter. All we are interested in doing is lessening the pH swing. This can most easily be accomplished by increasing the agitation in the tank so that the CO2 outgasses faster. I have a HOB, so I increase the flow. Those with canister filters could just as easily turn on a bubble wand at night.

Turning off the CO2 at night will also cause less CO2 by morning, but the problem here is your trading one pH swing for another (and possibly more dangerous). When you increase the agitation but maintain the same amount of CO2, you will have a steady, gradual decrease in pH. When you shut the CO2 off, you will very quickly outgas the CO2 (especially if you have a HOB). This will rapidly swing the pH higher. It will then stay high throughout the night, and then crash back down when the CO2 is turned on (and the crash will be directly related to your light level, and to your method/efficiency of injection). If you have low/medium light and a really efficient injection method (say 1wpg and a powerhead reactor, the pH will drop very rapidly. If you have high light and relatively inefficient injection (I think most of us DIY'ers have pretty basic injection), the pH will drop very slowly since the plants will be able to uptake much more CO2).

I'd rather have a slow, steady drop in pH, than a quick rise in pH, but that's just my opinion.

justin

 

[Wizzard~Of~Ozz]

My PH controller turns the tank on 3 times through the night to get the PH back down.. I don't see how my PH drops over night, infact it would probably be aroun 7.4 in the morning compared to 6.5 the controller pushes it to (I have 0 surface aggitation)