# Leaving CO2 on Overnight



## rocklobster (Jul 11, 2009)

I wanted to hear other opinions on this. I'm planning to set up a high tech planted aquarium in my 75G with a couple of discus.

Would it be a wise decision to leave the CO2 on all day, oppose to turning it off at night? I'm a little scared that the fish may require O2 if the CO2 is on overnight, and I'm a little hesitant of turning it off, and then on again because of the pH fluctuating everywhere.

Please share some insight :icon_roll


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## Chlorophile (Aug 2, 2011)

Okay - I'm sure someone will have better info on why the pH fluctuations don't matter, but I can tell you that basically fish don't care if the pH swings - its gh and tds that freaks them out. 
We do water changes which typically removes all the co2 and swings the pH drastically but the fish don't care. 

On big tanks I actually prefer to run co2 24/7.

You might find that you use less co2 as well. 
I have found that on my 20 gallon I can run 70 bubbles a minute and keep the drop checker a nice green all the time if I keep co2 on 24/7.

If I let it off gas I have to have the bubble rate around 3 bps and have my co2 come on a couple hours before the lights do for the drop checker to be green (yes part of this is the delay in the drop checker) and then towards the end of the day my drop checker is yellowing up which my shrimp don't like. 

Over all I have better results on that tank with running co2 constantly and its my opinion that I am using less co2 and probably stressing fish less. 

I have lots of surface agitation anyway and I don't push my drop checker into the yellow. 

I've found I have BBA issues if I offgas my co2 every night, and to compensate I need to crank it during the day - everyones experiences are different but you might find the same is true for you.

Another aspect to consider is that your tank is 75 gallons and good co2 distribution is hard in a large tank. And you also will be offgassing a LOT of co2 every night, and pumping a lot in every morning to get it back to your ideal level. 
I think you'd save a lot of co2 if you ran it 24/7


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## Joe.1 (Nov 23, 2009)

I leave my co2 on 24/7. It doesn't bother the fishes and shrimps at all. Plants and everthing else are growing fine.


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## endgin28 (Feb 9, 2010)

I have a different opinion on the co2 issue, although I run smaller setups than chlorophile. I used to run 24/7 co2 and had issues with fatalities. When I made the switch to one hour before lights come on to one hour before they go off and issues have been reduced significantly. One area of concern is with single stage regulators and end of tank dump. (excessive CO2 at night especially is problematic).
Also, there is an article on biochemical oxygen demand (BOD) on this site somewhere that makes a pretty strong case for not only running co2 just when the lights are on, but also for additional aeration at night. Basically it makes the case that you are helping your biofilter substantially by running this route. The fact that ADA recommends this route is a pretty strong endorsement, IMO.
I am not an expert by any means, but these two factors have encouraged me to go this route with my four pressurized tanks.


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## Chlorophile (Aug 2, 2011)

endgin28 said:


> I have a different opinion on the co2 issue, although I run smaller setups than chlorophile. I used to run 24/7 co2 and had issues with fatalities. When I made the switch to one hour before lights come on to one hour before they go off and issues have been reduced significantly. One area of concern is with single stage regulators and end of tank dump. (excessive CO2 at night especially is problematic).
> Also, there is an article on biochemical oxygen demand (BOD) on this site somewhere that makes a pretty strong case for not only running co2 just when the lights are on, but also for additional aeration at night. Basically it makes the case that you are helping your biofilter substantially by running this route. The fact that ADA recommends this route is a pretty strong endorsement, IMO.
> I am not an expert by any means, but these two factors have encouraged me to go this route with my four pressurized tanks.


I agree completely, but I've never had a co2 related fatality. 
I don't run my co2 very high, its just past bluish green, in the true green range on my drop checker
If you are running your co2 at a higher rate, pushing the drop checker into mountain dew ranges, then I wouldn't even think about leaving it on at night cause it will definitely go beyond that point.

Another thing to think about is plant mass, if you have a very high plant mass the amount of co2 being used is quite a lot so at night your co2 levels could rise quite a bit. 
Most of my tanks are low-medium light with moderate amounts of plants, but they are slow growers like ferns and anubias so they probably aren't consuming massive amounts of co2. 

I have tiger shrimp in my 24/7 co2 tank and they aren't phased. 
I ran 24/7 in my ADA Mini M and lost 7 super tigers on that very first night, I think it's because their was so much less water, it had an HC carpet that consumed lots of co2 during the day, creating a larger differential between day and night, and the lily pipe I was using didn't create enough surface ripple.

So IMO; 

If you're running high light, with lots of plants and you don't have a lot of surface ripple (all my tanks are way over filtered, my 20g has a 2211 2213 and AC 50 on it) then turn the co2 off at night, especially if you intend to push your co2 to the levels that make your drop checker start to yellow during the day or have very sensitive live stock 

If you're running low light and moderately planted in a 20g or larger tank - you might want to do 24/7 co2 - but that's again just my opinion.


Also about EOTD, I have pretty much eliminated EOTD by setting my working pressure to 55 psi. My Regulator has a safety valve that is set to trip at 60psi but in testing it actually trips at 57 psi, if my tank starts to empty and my working pressures rise my bubble rate is only increased by about 15 percent, and since my bubble rate is only around 1.1 per second, and my co2 isn't being pushed to the limit - I don't have much to worry about.


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## rocklobster (Jul 11, 2009)

Thanks for the awesome info!

I am planning to grow a carpet of HC Cuba, and I know they are very CO2 demanding. I'm going to try to aim for green on the drop checker, and observe it during the night with the CO2 on. If it's yellow over night (or if the HC Cuba isn't growing), I will probably plug the solenoid in.

I'm going to have some surface agitation from my spray bar (eheim 2028), and a power head. Hopefully that'll be enough so my fish don't die from lack of O2 

Does this sound okay, or should I try something different?


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## endgin28 (Feb 9, 2010)

HC does like a lot of co2. IMO emerald green is where you want to be. Put your powerhead on a timer aimed at the surface for night agitation, but keep your spray bar running with minimal agitation (not none, just not tons). Just one option.


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## Dini (Jan 5, 2012)

I run 24/7 on my 130 gal. and my CO2 is run on a PH controller. Albeit I have minimal fish in mine...maybe 20 and mostly Corries and Otto's. It isn't dutch but the plants take precedence over the fish. 

+1 to what Chloro said.


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