# co2 when the lights are off?



## cmiley (Mar 3, 2016)

Hello plant nerds,
I am determining weather or not to run my co2 only on the light cycle or to run it via a pH meter(set to come on every time the pH rises above 6.9) Are there any benefits to the plants if the Co2 is on when the lights are off? As the meter turns the co2 on according to pH this happens with or with out the lights on? Any ideas on which method is better for the plants. I assume that plants are photosynthesizing when the lights are on and this would be the best time to have the co2 on. However if the ppm of co2 in the tank remains constant then co2 is always there when the plants need it, right? Thanks in advance to any suggestions.


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## happi (Dec 18, 2009)

cmiley said:


> Hello plant nerds,
> I am determining weather or not to run my co2 only on the light cycle or to run it via a pH meter(set to come on every time the pH rises above 6.9) Are there any benefits to the plants if the Co2 is on when the lights are off? As the meter turns the co2 on according to pH this happens with or with out the lights on? Any ideas on which method is better for the plants. I assume that plants are photosynthesizing when the lights are on and this would be the best time to have the co2 on. However if the ppm of co2 in the tank remains constant then co2 is always there when the plants need it, right? Thanks in advance to any suggestions.


its better to have the co2 turn on 1 hour ahead of lights, so you could have enough co2 for plants to use soon as lights switch on. i wouldn't recommend leaving the co2 on when lights are not on.


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## IUnknown (Feb 5, 2003)

I let the controller keep the ph stable. Co2 is produced at night, so the controller would not activate the Co2 anyways. I've read that having stable ph is better on the bacteria colonies then having big swings every day.


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## Edward (Apr 11, 2005)

CO2 24/7, set it and forget it, simple.


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## AWolf (Jun 13, 2014)

I'm still looking for an article/graph I saw where it measured photosynthesis 24hrs light and dark by the hour. I believe it showed that photosynthesis rose in the morning, like the sun, using the most CO2 later in the day and evening, even after the light went down for a while. Morning less use, midday starting to climb, afternoon and evening a couple of hours into night the highest CO2 use, then it dropped drastically at midnight or so......the best of my recollection. I remember because it was interesting to know that you could do without CO2 until later in the day, and keep it on until midnight. Problem is, I can't find the article. Most graphs show photosynthesis in general from sun up to sundown. Not specifically CO2 usage, like this article did. 

If anyone finds this, be sure to post it! I could be totally wrong about this. Memory can be tricky.


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## Hoppy (Dec 24, 2005)

The plants won't mind having the CO2 on 24 hours a day, and if you don't try for more than 20-30 ppm of CO2, the fish shouldn't be bothered either. Much more CO2 than that and it might be too much for the fish at night, when the plants aren't using any CO2. In any case, the pH controller should prevent any big problems. This wastes CO2, but it is cheap anyway.


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## IUnknown (Feb 5, 2003)

Awolf,
Here are the graphs from my apex measuring ph. The 3/03 pic shows my inline reactor injecting a stable 30ppm into the tank. Problem was it couldn't keep up with demand, so by the end of the day I was down to 15ppm. The 3/05 pic shows what it looks like after installing a cerges reactor and increasing my bpm so that it injects more than 30ppm and lets the controller turn the co2 off when its more than 30ppm.

The 3/03 graph coincides exactly with my lights. As soon as the lights turn on, photo-respiration starts, and vice versa.


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## AWolf (Jun 13, 2014)

IUnknown said:


> The 3/03 graph coincides exactly with my lights. As soon as the lights turn on, photo-respiration starts, and vice versa.


Thanks! That is good to know. I wonder why I thought CO2 uptake was still going on strong for a couple hours after lights out? Oh well, memory...Probably from bashing my head against the wall watching the Presidential debates.


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## Straight shooter (Nov 26, 2015)

In nature photosynthesis is generally highest in the mornings due to plant respiration over night influencing CO2 concentration. Photosynthesis slows as CO2 is depleted during the day. It is common to see big pH swings in 24hr periods in nature due to CO2 levels rising and falling. The notion that injecting CO2 only for the photoperiod causes severe pH swings that fish would not be subjected to in nature etc is a misconception.


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## dzega (Apr 22, 2013)

i switch off co2 at night only to save on gas (i turn it on early in the morning more that 2h ahead of lights). i believe its better to have stable HP the whole time. you wont gasp your fish with ph controller at night


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## cmiley (Mar 3, 2016)

so I am to understand that pH swings are not an issue. It has been bothering me when I watch the pH travel from 6.6 to 7.2 through out the day. Is this not a problem? Also with running the gas that long will the pH continue to fall? Doesn't a really low pH affect the biological filter and the micro organisms in it?

Bump: in addition as I understand from reading on this site that pH is not as important to plants as it is to fish. Will the plants be affected by pH shifts?

Bump: one more question how to you measure co2 in part per million? is there a test kit? I have not seen one. Once again thank you for all y'all for the information it is much appreciated.


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## rick dale (Feb 26, 2014)

*Co2*

I run a fairly heavily planted tank. 60 gallons. I use a pH controller , which I absolutely love. I turn it on when I leave for work , about 7 in the morning , and turn it off about 6 in the evening. This is only to save gas. Yes it's cheap , but it's also kinda a pain in the butt to go get it refilled. Plus , Alli have to do Is punch the red button on the controller to turn it off. And if I forget it , that's no big deal either. Just make sure you have the drop in pH you want before the lights come on. Running it all night will not make your plants any better or worse. You just don't want the fluctuation while your lights are on , and the pH controller will take care of that.


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## Straight shooter (Nov 26, 2015)

pH controller isn't necessary, it's a luxury item. A timer is what I use, CO2 on before photo period and turns off around 45mins before lights out. No need to inject CO2 outside of the photoperiod if you can avoid it. 

Very basically, to inject 30ppm CO2 often a full 1pH drop during the photoperiod may be required. 7.2-6.6pH drop seems normal and healthy for a CO2 injected tank. You may be able to increase CO2 a little further if your livestock don't mind.

Accurately measuring CO2 concentration at hobbyist level can be difficult. The test kits are almost useless. I use a pH pen to estimate CO2 concentration. 

As I said earlier, most fish don't mind a significant rise and fall of pH due to CO2. This happens in nature also.


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## PortalMasteryRy (Oct 16, 2012)

cmiley said:


> so I am to understand that pH swings are not an issue. It has been bothering me when I watch the pH travel from 6.6 to 7.2 through out the day. Is this not a problem? Also with running the gas that long will the pH continue to fall? Doesn't a really low pH affect the biological filter and the micro organisms in it?
> 
> Bump: in addition as I understand from reading on this site that pH is not as important to plants as it is to fish. Will the plants be affected by pH shifts?
> 
> Bump: one more question how to you measure co2 in part per million? is there a test kit? I have not seen one. Once again thank you for all y'all for the information it is much appreciated.


You can purchase a liquid titration kit for testing CO2.

HI3818 Carbon Dioxide Test Kit - Hanna Instruments
I have used this kit and I don't know if it is accurate. My last test indicated that I have 60 ppm CO2 at peak of the injection.

The other method is using the PH/KH/CO2 chart. Assuming you can accurately measure your KH then you'll get a good estimate of your CO2 levels.


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## cmiley (Mar 3, 2016)

thanks for taking the time to answer my questions.


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