# Leaving CO2 on at Night



## jamezgt (Feb 17, 2009)

So I'm planning to convert my 75G to a heavily planted tank with Discus, and I'm deciding whether or not I should leave or turn off the CO2 injection at night.

I'm scared that by turning off the CO2 at night it will cause a pH swing (TDS) and kill the Discus. I've heard stories that people have lost their fish because of this, but it's quite rare.

But if I were to leave the CO2 on over night, there is a possibility of gassing the fish, and actually waste CO2 over time. I was thinking of leaving the CO2 on over night, and adding an air stone when the lights are off to prevent gassing of the fish.

I'd love to hear people's advice on this situation :]


----------



## ameekplec. (May 1, 2008)

Are you using the CO2 just to control the pH of the water?

If you are, I'd just invest in a pH controller - so whatever the light cycle, the CO2 will only flow when you need it to bring down the pH. Milwaukee makes the cheapest ones, and they do just fine:
http://www.jlaquatics.com/phpstore/store_pages/product-info.php?product_ID=mil-cntph

$120


----------



## jamezgt (Feb 17, 2009)

ameekplec. said:


> Are you using the CO2 just to control the pH of the water?
> 
> If you are, I'd just invest in a pH controller - so whatever the light cycle, the CO2 will only flow when you need it to bring down the pH. Milwaukee makes the cheapest ones, and they do just fine:
> http://www.jlaquatics.com/phpstore/store_pages/product-info.php?product_ID=mil-cntph
> ...


I'm planning to have high CO2 levels because I'm going to try to grow HC Cuba. Would I have to adjust the pH controller to a lower pH to achieve a higher amount of CO2 then?


----------



## ameekplec. (May 1, 2008)

jamezgt said:


> I'm planning to have high CO2 levels because I'm going to try to grow HC Cuba. *Would I have to adjust the pH controller to a lower pH to achieve a higher amount of CO2 then?*


Yes.

And at night, it'll only inject CO2 to keep the pH constant, but it probably won't need that. If you're really concerned about oxygen levels, have a powerhead set to turn on if the pH drops below a certain level.


----------



## jamezgt (Feb 17, 2009)

ameekplec. said:


> Yes.
> 
> And at night, it'll only inject CO2 to keep the pH constant, but it probably won't need that. If you're really concerned about oxygen levels, have a powerhead set to turn on if the pH drops below a certain level.


Good info!

Unfortunately, $120 is a lot to invest into the setup right now 

If I didn't have a pH controller, but a solenoid, what would you recommend doing?


----------



## ameekplec. (May 1, 2008)

I would just turn off the CO2 at night. Chances are in a highly planted tank, you'll get enough respiration throughout the night that your pH swings won't be too bad.


----------



## J-P (Feb 27, 2011)

That's odd... when I had my tank it was the opposite. I left the CO2 on 24/7. At night since the plants were not taking up the CO2 I got water acidification. The pH dropped like a stone. During the day when there were lights the pH would rise again.

I kept my tank lights on from noon -10 pm. It was that after 10 PM the ph would drop and creep back up again around 6 or 7 am (from natural ambient light).

When it did drop it was almost 1.5 points ~ 2 points.


----------



## HOWsMom (Jan 3, 2012)

jamezgt said:


> I was thinking of leaving the CO2 on over night, and adding an air stone when the lights are off to prevent gassing of the fish.


That is what I'm doing right now.

But, I'm doing it because my needle valve is so finicky that I don't want to deal with it every day - and I cannot afford a solenoid


----------



## ameekplec. (May 1, 2008)

J-P said:


> That's odd... when I had my tank it was the opposite. I left the CO2 on 24/7. At night since the plants were not taking up the CO2 I got water acidification. The pH dropped like a stone. During the day when there were lights the pH would rise again.
> 
> I kept my tank lights on from noon -10 pm. It was that after 10 PM the ph would drop and creep back up again around 6 or 7 am (from natural ambient light).
> 
> When it did drop it was almost 1.5 points ~ 2 points.


That's what usually happens in most tanks!  but I guess if you're pumping a lot of co2 without lots of plants maybe you won't get enough co2 to bring the ph down?


----------



## Stephen (May 6, 2011)

During the day plants take in co2 and use light. (photosynthesis)
At night they give off oxygen and completely stop using co2.

Think of what you are doing to the tank.
During the day plants will suck the co2 even if you don't inject it. At night it will give off the oxygen. Thus allowing your fish to breath. 
So now you leave it on at night and you will be mixing oxygen with co2. I am pretty sure you will find your oxygen level much less. Don't fight nature. 

In nature there is a natural ph swing between night and day. 
You will not kill your discus if you have a heavily planted tank. I have a decent idea of what I am talking about as I am raising discus fry in a heavily planted tank of hc and christmas moss.
During the day I have co2 going in at a rate of about one bubble a second. The co2 turns off at night.

By leaving the co2 on at night you will likely do a lot more harm then turning it off. You can effect the water negatively.
I would suggest against high amounts of co2 if you are looking to keep fish of any kind in the tank.
1-2 bubbles a second in something like a 20 gallon no more. Small tanks like a 10 gallon and smaller no more then 1 bubble per second.

You can make a nice carpet without big amounts of co2. It is not strictly necessary to grow hc anyway. It will grow slower without injection but it will grow just fine none without it.


----------



## Darkblade48 (Jan 28, 2008)

Stephen said:


> During the day plants take in co2 and use light. (photosynthesis)
> At night they give off oxygen and completely stop using co2.


Plants respire at night, and do not give off oxygen. Production of oxygen is a result of photosynthesis, not respiration.



Stephen said:


> At night it will give off the oxygen. Thus allowing your fish to breath.


See above. Plants do not produce oxygen in the absence of light.



Stephen said:


> So now you leave it on at night and you will be mixing oxygen with co2. I am pretty sure you will find your oxygen level much less. Don't fight nature.


The injection of carbon dioxide does not displace oxygen.



Stephen said:


> 1-2 bubbles a second in something like a 20 gallon no more. Small tanks like a 10 gallon and smaller no more then 1 bubble per second.


This depends on your plant load. I would recommend that you have a drop checker with a 4 dkH reference solution to ensure that you have approximately 30 ppm of carbon dioxide in your water column. The rate at which you inject carbon dioxide will be dependent on your plant load and the type of plants you have.



Stephen said:


> You can make a nice carpet without big amounts of co2. It is not strictly necessary to grow hc anyway. It will grow slower without injection but it will grow just fine none without it.


In my experience, HC does best with carbon dioxide injection. Without it (i.e. using glutaraldehyde) will also work, but there is a marked difference.


----------



## Stephen (May 6, 2011)

alright yes they don't release oxygen at night they use it. 
They will release co2. 

I did say you would notice a growth difference without co2 when growing hc. But it will grow.
You are right it does best with it.


I was mainly trying to advise the op against leaving the co2 injection on at night.


----------



## Kooka (Feb 8, 2011)

Just say *NO* to CO2 at night. It's pointless. If your tank is planted, the plants will give off CO2 due to respiration, therefore keeping your tank's pH level in check. Don't worry, be happy, and enjoy your discus!


----------



## tankies (Feb 1, 2012)

and how do you stop co2 with diy co2 generator(yeast)?
thinking, an air pump on a timer turns on at nite?


----------



## Darkblade48 (Jan 28, 2008)

tankies said:


> and how do you stop co2 with diy co2 generator(yeast)?
> thinking, an air pump on a timer turns on at nite?


You cannot stop the CO2 production if you are using DIY CO2, but you are correct in that you can drive off excess CO2 with an air pump.


----------



## tankies (Feb 1, 2012)

Darkblade48 said:


> You cannot stop the CO2 production if you are using DIY CO2, but you are correct in that you can drive off excess CO2 with an air pump.


precisely, that was the point of the question....most of the discussion referring to pressurized co2 where control is possible.


----------



## charlie1 (Dec 1, 2011)

tankies said:


> precisely, that was the point of the question....most of the discussion referring to pressurized co2 where control is possible.


 I`m confused, were you asking the question for your knowledge or were you insinuating the OP had a sugar & yeast generator?


----------



## tankies (Feb 1, 2012)

charlie1 said:


> I`m confused, were you asking the question for your knowledge or were you insinuating the OP had a sugar & yeast generator?


Im not insinuating. I was agreeing with darkblade. I was merely stating that for pressurized system, its convenient and easy to turn on/ off co2 unlike the diy(yeast) generator.


----------

