# When to turn off CO2?



## willknowitall (Oct 3, 2010)

would depend on light and density of plants


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## WATduh (Feb 27, 2011)

Nev-ah! I run mine 24/7. I have a low bubble and pressure rate. Keeps a constant CO2 level in the tank with no fluctuations. 

If you do choose to shut it off, a lot of people shut off right when the lights go out and get it running again 1-2 hours before they click on.


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## Wasserpest (Jun 12, 2003)

It's not going to be exact science... if everything else is running well, an hour plus or minus isn't going to make a big difference. So go ahead and pick some number, and stick with it for a while to see if it works.

I too chose to turn off CO2 an hour before lights out, and back on an hour before lights on. Haven't done any exact measurements, and even if someone does, it will be hard to exactly know how it affects our plants.

(This could be different/important if you are running CO2 at max-fish-gasping level for some reason... I don't).


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## VeeSe (Apr 16, 2011)

I'm lazy and have it on the same timer as my lights, so it comes on right when lights come on and goes off right when the lights go off.


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## sampster5000 (Oct 30, 2010)

I recommend at least 30 minutes before you turn off the lights. You dont want to risk losing any tank inhabitants. I'd also turn on any air pumps at the same time.


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## 150EH (Dec 6, 2004)

Mine comes on 1.5 hours before the lights and 30 minutes before lights out, I don't really see any difference with the exception that, if I don't build up enough before lights on it seems the tank is playing catch up all day to get enough C02, but once there is enough before lights on the DC is lime green all day.


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## Aquaticfan (Oct 30, 2011)

I turn mine on 1 hour before to pre-load the water before the lights come on. The things that drive this would be your plant density, Water flow in the tank and how intense you lights are. if you have a medium light tank vs a high light or Very high light its going to be different. Same with the amount of plants. More plants mean it will be able to consume more. For some people's tanks to have the full effect from Co2 and balance it could vary in time that it all comes on. For some its same as the lights or 30 min before or 1 to 1.5 hours before. 

As far as turning off goes..... I normally go for at least 30 min. Reason you want to give it a little time is you can have Co2 in the line as well as sometimes it can take a little for the solenoid and such to close off fully. The time difference allows that and allows the system to no longer pump Co2 into the water. Really, the off gassing and final consumption by the plants happens pretty quick. Normally 30 to 45 minutes and your Co2 levels will be back to about nothing. I dont believe in adding air via pump and stone back to the water either. Just let it off gass and it will be fine. Havent lost any fish to this. Alot of what makes it again off gas faster is current, If you have a surface ripple and plant density. 

But as Wasserpest said above its not going to be an exact science for everyone. To many variables to account for.


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## spookyspike (Aug 13, 2011)

Slightly off topic but still related, if you are using a DIY C02 set up, I assume you cant turn that off so its just left to run 24/7? Sorry to jump in on your thread.


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## denboka (Dec 2, 2011)

I just recently switched from DIY co2. It ran 24/7. I think the main reason to turn off the co2 with pressurized, is to save co2. Plants don't need/use co2 at night, so you would be wasting it at night. In nature co2 is there 24/7.

I was just wondering when most people turn theirs on. I will leave mine at 1hr before on/off and watch the effects. 

Thanks for the input all!!


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## ChadRamsey (Nov 3, 2011)

i have my lights and my co2 on the same timer. they come on together and go off together.


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## ktownhero (Mar 21, 2011)

CO2 timer is offset an hour behind my Lights, so an hour early for both on and off.


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## zergling (May 16, 2007)

12PM - CO2 starts
2PM - Lights start
10PM - Both CO2 and lights go off.

This is for my ADA 120-P (a little over 64gal). I'm running reef-worthy T5HO lighting, so I have to HAVE CO2 really high, otherwise algae will just take over. 

For smaller tanks and/or much less intense lighting, there's much more leeway.


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