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Why do we aim for 30 ppm CO2?

John P Coates

John P Coates

Member
Joined
21 Feb 2014
Messages
164
Location
Bracknell
Hi folks,

I get the impression that 30ppm is the target CO2 concentration in planted aquaria. If what I say is correct, why is 30 ppm CO2 considered optimum?

Looking at the Tropica aquatic plants website, I see that many, if not most, plants are happy with less than 15ppm. That being so, I am inclined to aim for 15ppm in the new tank that I am setting up. But then there will be implications, some of which I've already thought of being:

1 Do I need to adjust my drop checker to 2°dH instead of 4°dH?

2 Do I need to switch CO2 off at night?

3 My CO2 cylinder should last longer.

4 Lower CO2 should be better for the fish.

Am I overlooking something?

JPC
 
Hi,

Most tropica plants has the "15" because that's "easy" plants to keep ( do not need souch lite to grow ). More light = more CO2 uptake. How Nathaniel said 30 is satisfy amount for plants and your fish does not suffer. However all this are just numbers you should see how fish and plants doing. Anything above 30 can harm your fish...

1 sorry no idea
2 yea you should if you do not want to turn you fish tank to gass chamber and kill everything. However if you want to run it in night as well the you will need to run air pump too
3 yes that's another reason why switch it off
4 yes but it is not harmful below 30

Vaz
 
Also bare in mind that most peoples disasters with planted tanks is with co2 levels and distribution. So 30ppm and off at night had been proved time and time again, so tread carefully.
 
The CO2 concentration depends on the amount of light. 30 ppm is just about ideal for tanks with medium light.
I also keep my CO2 constant 3+ bps forever.
 
Ian Holdich said:
And also keep your c02 consistent...I've found this probably the most important part.
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Hi Ian,

Many thanks for your reply.

What do you mean by 'keep your CO2 consistent'? Does this mean that I need to ensure the CO2 ppm does not vary - is that correct? If so, how do I achieve this overnight? Should the CO2 be switched off overnight? And, if so, what about the pH swings?

JPC
 
No, he means constant CO2 ppm during lights on time.

So you turn CO2 on say 2 hours before you lights to allow level to reach say 30ppm (green drop checker). You keep 30ppm (green drop checker) until about 1hour before lights off.

During lights off the CO2 will disperse, faster if you use an air stone, but as lights are off plants (& algae) don't make use of CO2.

Some people, especially with smaller tanks, run CO2 24/7, again constant ppm during lights on, but obviously wasting CO2 during the night.
 
Yes, once you have your c02 at a stable level, leave it at that. It should be off at night, this is why we use solenoids. Then you don't have to touch it at all.
 
Aquadream said:
The CO2 concentration depends on the amount of light. 30 ppm is just about ideal for tanks with medium light.
I also keep my CO2 constant 3+ bps forever.
Click to expand...
Hi Aquadream,

Are you able to put a (PAR) figure on 'medium light'? My point about 30ppm CO2 is that it is twice the figure required by many plants, according to Tropica. So, if nothing else, we are subjecting our fish to twice the CO2 concentration than may be necessary. And we're wasting CO2.

I note that you don't switch your CO2 off overnight. That's what I would prefer to do.

JPC
 
harryH said:
But surely there's no bigger waste of CO2 than to run it overnight when your plants no longer need it?
Click to expand...
Hello Harry,

Fair point. But, as with a lot of things, it's a question of finding the right balance, isn't it? So, if I have to waste CO2 overnight but it's better for the fish because the pH is more stable, which would I choose? That's why I'm interested in the target CO2 concentration of 30ppm. Because, overnight, the CO2 concentration will increase if not switched off and perhaps attain unsafe levels. So, we have to switch the CO2 off using a solenoid valve. But if the target concentration of CO2 during the day was, say, 15ppm, we may be able to leave CO2 on overnight with no risk to the fish and pH may be sufficiently stable. I don't know the answer to this, which is why I started this thread. From what I have read, it just seems to me that the choice of 30ppm CO2 is somewhat on the high side.

JPC
 
Hello John, well we are all learning and I can only relate my own method.

I have always attempted to get my CO2 to a maximum acceptable level during daylight hours, once there I aim to keep that level by, as Ian says above leaving the regulator alone.

There are of course so many factors which is why tanks differ in their requirements one to another and why I remarked keeping a consistent level is not always easy. Number of plants, lighting, flow distribution etc but as plants give off CO2 at night, oxygen levels can be greatly reduced. I would never think of lowering the CO2 during the day so that I can run it overnight. Better to aim for the mythical 30ppm during the day and switch off at night, using the method of having CO2 come on an hour or even 2 hours prior to lights on and going off before lights out.

If you have a spray bar or power head causing a ripple effect of the water surface, oxygen levels can be maintained at night.

I have to admit I used to always have my CO2 on 24/7 years ago but do feel I have more control over it these days via a solenoid plus it's greater economy is a big consideration especially on large set-ups.

Harry.
 
harryH said:
Hello John, well we are all learning and I can only relate my own method.

I have always attempted to get my CO2 to a maximum acceptable level during daylight hours, once there I aim to keep that level by, as Ian says above leaving the regulator alone.

There are of course so many factors which is why tanks differ in their requirements one to another and why I remarked keeping a consistent level is not always easy. Number of plants, lighting, flow distribution etc but as plants give off CO2 at night, oxygen levels can be greatly reduced. I would never think of lowering the CO2 during the day so that I can run it overnight. Better to aim for the mythical 30ppm during the day and switch off at night, using the method of having CO2 come on an hour or even 2 hours prior to lights on and going off before lights out.

If you have a spray bar or power head causing a ripple effect of the water surface, oxygen levels can be maintained at night.

I have to admit I used to always have my CO2 on 24/7 years ago but do feel I have more control over it these days via a solenoid plus it's greater economy is a big consideration especially on large set-ups.

Harry.
Click to expand...
Hi Harry,

Thanks for detailing your method of controlling CO2. Your feedback is very useful.

John C.[DOUBLEPOST=1396451857][/DOUBLEPOST]
ian_m said:
http://www.practicalfishkeeping.co.uk/content.php?sid=5264
Click to expand...
Hi Ian,

Thanks for the link to the excellent article. It makes for very interesting reading and it addresses many of the issues that were whizzing around in my mind.

John C.
 
Last edited:
Vazkez said:
Hi,

I know this does not answer your question, however if you wnat ot keep just the "easy" plant you better go low tech (withoud CO2) and saveyourself lots of trouble 🙂
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Hi Vaz,

On the contrary, it's no trouble at all. As a scientist, I have an enquiring mind. I like to understand exactly what's going on 'under the hood'. No stone left unturned and all that. I have no wish to stay with just the easy plants. The thing is that I had a four year break from aquarium fishkeeping and now I can't get enough of it. So, if there's something I don't understand, I ask. I've successfully grown (with CO2) quite a few aquarium plants before. I wouldn't dream of keeping fish without live plants - they are beautiful and an important part of the aquatic ecosystem.

John C.
 
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