# Should I run CO2 constantly??



## Borntofish (Nov 30, 2007)

Hi All,
When I orginally set up my planted tank, I was advised to only run my CO2 while the lights are on since plants reverse the process at night and actually give off CO2. I have my current sytem hooked up to both the light timer and a pH monitor that turns the CO2 off if/when the pH reaches 6.8. Recently, someone suggested that I leave the CO2 running all the time? So which is it? And why run it all the time, so the pH doesn't change and thus the fish are happier??


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## davemonkey (Mar 29, 2008)

If you have it hooked up to a pH monitor, that's all you need. You'll be wasting CO2 at night running it 24/7, but it keeps the CO2 levels constant so it's readily available at "lights on". There is alot more discussion on this in the "APC polls" section. Look for one titled something like "CO2 timed with lights or 24/7".

-Dave


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## Zapins (Jul 28, 2004)

I leave it on 24/7


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## Bryeman (Aug 24, 2009)

On my 125g, I have two canister filters each with their own CO2 tank. One is hooked up to a pH monitor and the other runs constantly, but at a much slower rate. This system has worked wonders in my tank. The pH doesn't move during the night, but when the lights come on and plants start consuming CO2, the pH goes up and the other bottle kicks in once the selenoid valve turns on (the bubble rate on this tank is much higher than the one running constantly). 

I'll never do it any other way. I also know that I'm getting excellent CO2 distribution since I have two bottles going and the canister filter outfeeds are spread out!

To answer the question though, mine runs constantly. I did the turn off at night thing on other tanks, but the pH swing on those tanks got kind of wild, but just my own experience.


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## snail_chen (Dec 4, 2009)

I have a pH controller and a timer in combination. It is definitely a waste to inject CO2 at night since no plants can photosynthesize. Plus both plants and fish exhale CO2 at night.


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## geeks_15 (Dec 9, 2006)

It can be done either way with good results. If you look through threads on this topic you'll find arguments for both. There are minor positives and negatives to both approaches, but as long as your tank is going well I would just keep doing what is working.


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## hariom (Sep 2, 2008)

I have tried both options. I have hard water with a ph of 7.6 in Savannah and have a 3/4 bubbles/sec rate. I inject it through a power head with pressurized co2. (did a DIY experiment by punching holes into the impeller blades) Leaving it on 24x7 for me helps me keep the BBA at bay. The ph though does drop to 6.7 in the night with co2 on. It climbs to 7.1 when the lights are on. I though had to monitor my fish for the first entire night to see that they were not suffocating. 
I was reading reviews a couple of months ago on this same issue and decided to shut off 1 hr after the lights and 2 hrs before the lights came on. I had a massive re-occurrence of BBA on tank walls and on plants. After this, no matter how much co2 is wasted, I cannot afford such destruction to my tank. For some reason my tank doesn't like the CO2 off in the night.

I have also seen my rotala macranda 'green' growth slowing down with co2 24x7. The growth almost triples with the no co2 in the night. My Pogostemon stellatus 'Broad' though is the exact opposite of this.


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