# Should I run my CO2 at night?



## Wasserpest (Jun 12, 2003)

There are different schools of thought here. My thoughts --

If you already have a solenoid, there is nothing wrong with running CO2 with the lights only. It will save CO2, and prevent excessive CO2 levels at night. Some think the CO2 should be up to max levels when the lights go on. If you think that makes sense, then you could run CO2 on a different timer, to have it start bubbling maybe an hour before lights turn on.

PH changes due to CO2 aren't an issue... it's the CO2 itself that kills, not the pH changes.


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## kevmo911 (Sep 24, 2010)

Fluctuating CO2 levels do not cause algae. Low CO2 levels with higher lighting will cause algae. Just make sure that when your lights are on, the CO2 is pumping.

I agree with Wasser - and many many many others - on the pH swings due to CO2 not harming fish.

Easiest method is To plug the solenoid and lights into the same timer. I have mine plugged into a strip, which is plugged into the timer. Yes, some people have CO2 come on a little while before lights, but I've seen little or no actual data on whether this does anything at all.

Oh, and maximizing your CO2 during your lighting period, unless you have a serious nutrient lack, will all but eliminate algae issues. With medium light and a Mountain Dew colored drop checker, I literally haven't had to use my Mag-Float to scrap algae in a couple months on my 30g. Then again, a few otos, a couple BN Plecos, and a few nerites probably help with that.


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## talontsiawd (Oct 19, 2008)

It doesn't affect plant growth from my experiences at all. It doesn't harm the fish in my experience either. The only thing is if you have a HOB filter, it will out gas your CO2 at night which may be better for the fish (I don't think it really matters personally), and your CO2 levels will be lower when the lights come on (again, I don't think it matters personally)

I know that a drop checker isn't the most accurate thing and it takes a long time to change color. I will say this though. With my CO2 only on when the lights are on, my drop checker would go to almost blue with HOB filter. With my canister, it is the same color as when the lights go off. It can stay in the green for atleast 48 hours when the CO2 runs out. 

I bring this up because with a canister filter, it seems that the co2 stays diffused in the water for quite a bit of time, according to my drop checker (and backing this idea up when I have used a HOB filter alone, or inconjunction with my canister). My point is, even a solenoid may not help high CO2 levels at night. It isn't going to hurt it, I am not convinced that CO2 levels change much at all when you don't have anything to help out gas it quickly. 

At the end of the day, I think a solenoid is best to save CO2 and that's all I would count on it to do. My CO2 is on for 7 hours, about 1/3 of the day. It saves me money, that's why I use it.


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