# Can I keep the CO2 running 24 hours a day?



## Victor

So, the title tells all . I just need to know if there are some problems if I keep the CO2 running even during the lights off.


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## darren636

Stick your head in the oven and turn on the gas,   you'll get the same kind of outcome


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## Victor

So, I'll harm my plants? How?


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## Sacha

I'd be more worried about your fish than plants. You'll turn your tank into a gas chamber


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## Victor

But my DC never turns yellow, even during the night. It's always green. Perhaps the CO2 could kill some beneficial bacterias?


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## ian_m

Not a problem, as long as CO2 injection rate is not monsterously high. Local fish shop has some nice small planted tanks running CO2 24/7 no issues. If worried put an air pump on during dark hours.


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## Victor

I'm using about 1-2 bps in a 300 L tank. Now it's little planted but I plan to get a heavily planted tank. Do you think this CO2 rate is ok at moment?


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## bogwood

Hi. here are my own thoughts.

I was always under the impression it was unnecessary for several reasons.
However im sure the experts, will correct me, if im wrong.

COST. .....I run mine for  8hrs only a day, so my bottle lasts 3 times as long, saving time and money with refills.
LIVESTOCK..... I always worry about them getting too much particular at night, when im not there., so this helps them, in particular Shrimps.
PLANTS.... are thriving still.
LIGHTING.FERTS.....can be lower, so i can manage the growth rate of plants.

Not sure on your BPS, there are several factors to consider. Mine is approx 1BPS in 80 ltrs, and heavilly planted. 
Click on my link to see the tank.

Hope this helps a little.


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## Sacha

1-2 bps is nowhere near enough in a 300 litre tank.


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## Spnl

1-2bps? I wish! I run an uncountable bubble rate and still don't get high enough levels despite now achieving near 100% dissolution .

Re your question.  Very interesting.
Why would the fish be gassed at night if not during the day?

When we add CO2 to a tank we reduce the concentration gradient of CO2 across the gills of the fish, making it harder for the fish the excrete CO2. This causes a situation analogous to respiratory acidosis in mammals, usually due to lung disease impeding gas exchange. Animals compensate for the acidosis caused by too much CO2 in their blood by excretion of carbonic acid through kidneys, but this takes days to stabilise. I assume the same happens in fish.
This acidosis causes the Bohr effect, which means in acid conditions it is harder for haemoglobin to take up oxygen. 
So if oxygen levels fall while CO2 is high then the fish would suffer.

Do oxygen levels fall significantly at night? I don't know.  Planted tank people make a big thing of the O2 produced by plants during the day, but how significant is that?
Possibly not very significant for the following reasons
1. We are advised to turn the CO2 on a couple of hours before lights on, this would be the point of lowest oxygen conc. in the water if photosynthesis was the main source . Fish seem ok.
2. Heavily stocked tanks such as Rift Cichlid tanks or LFS tanks seem well oxygenated without any plants, though they don't have CO2 either.

So I would guess if the fish are fine during the day then they will be equally fine at night .
And, with processes that require gradual compensation like acidosis you might expect constant conditions to be beneficial compared to massive diurnal swings. For most things we try to keep conditions in our tanks stable.

There was a thread recently by alanyussupov (I think) in which he showed his tank with 24hr CO2 (that is from memory, please correct me if I am wrong)and his fish were fine. Plants were to die for. But if I remember  rightly he used a low bubble rate.

Of course the critical thing would be to make sure levels of CO2 are stable and not progressively increasing over time, that would be disastrous.

So maybe the main reason for turning CO2 off at night is really to avoid waste. Just my thoughts. I think many will violently disagree with this.
Btw, I turn my gas off at night.


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## milanioom

I've been keeping co2 on 24/7 for a year now with no problems. Obviously the cost is a bit higher, but I don't mind.


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## Michael W

I wouldn't put CO2 on for 24/7. For me, plants are there to help the livestock, I wouldn't want to put them in an unnecessary risky position for the plants sake which is why I opt for the low tech approach.Although, one can argue that by having the CO2 on for 24/7 but having just enough output to ensure livestock will be fine and yet have the benefit of healthy plants will provide a nice environment for the fish. But then wouldn't the CO2 need to be increased overtime as the plant mass grows to ensure the CO2 will reach/be enough for the extra growth and therefore increasing the risk for livestock at night?


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## Jafooli

When I first used DIY CO2 with yeast. I would stick an air pump on over night. I just thought it made sense to make sure there was enough oxygen. I now know I can just use surface agitation.
I could never get to sleep with my air pump but I put up with it, I did so much research on do I need an air pump with DIY CO2 etc and I never found an exact answer, as everyone is different.

However when I went to pressurized I lowered my surface agitation to help CO2 levels, and my regulator came with a solenoid! So I decided no more air pump.
I already new from various research the best time to tell if fish are struggling is around 5-6am in the morning, I'm normally a sleep then so was a bit hard to check that.

When I somehow woke up around them times, I noticed all my fish in the top right hand corner next to my filter, all together. They wasn't gasping or nothing. They was either there because there is hardly any flow there or its where the most oxygen was, being close to the surface and out of the direct flow from the filter.

Another time I've checked when I've increased surface agitation, they have all been at the substrate, some at the middle, just all dotted around. So I presume if your fish are acting fine at 5-6am in the morning then there's your answer. I would not feel comfortable leaving my CO2 on over night, the plants and fish are competing for oxygen, but I read adding CO2 don't drive oxygen away and both remain in the water so I guess its more to do with your tank oxygen levels rather than leaving CO2 on 24-7. Either way I would want my CO2 levels to be falling at night rather than rising.  My fish now remain at the bottom-mid level of my tank all night long. I'm happier with them there than being just below the surface.


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## NatureBoy

I trialled it for a about 6 weeks, no benefit really. Massive downside is you cane the CO2. Now I just inject for about 5 hours in the morning, mainly before lights on and limited surface agitation results in about the same thing


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## iowphil

I'm new to co2 injection so maybe my comments are justified with experience 
I have my lights ( twin 24w t5) come on at 4pm and go off at 10pm, 
In this time I have my co2 come on at 3pm and off at 9pm.
I haven't played about with other timing but my plants seem to be thriving from it with lots of colour and growth, 


Sent from my iPhone using Tapatalk


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