# Fluctuating CO2



## MrMacey (20 Jan 2014)

Hello everyone, this may seem a bit stupid as I have little knowledge on the matter but how does the fluctuation of CO2 (like when using the yeast method) affect the growth of algae? I have read that even though we aim for around 30ppm, plants use no where near all of this. So say if I was using yeast to produce to CO2 which started off at around 30ppm then gradually decreased to say 20ppm over the course of a week or two, would this still be sufficient for the plants providing that the nutrients and flow was up to scratch? I understand that the algae will be able to respond quicker to the change, however there will still be plenty of CO2 available for the plants to work at there max meaning there surely should be no difference?


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## Spnl (20 Jan 2014)

Hi
Not sure why you think plants don't use 30ppm. The plants we buy are mostly grown emersed, in atmospheric CO2 which is pushing 400ppm, we put them under water and they struggle to adapt for a while, in 1-3ppm with no CO2 supplement . 30ppm is as much as we can use without harming fish, it is a compromise, not abundance!
Does fluctuating CO2 cause algae? Lots of threads on here about it, some don't think it does.
But my experience is that BBA is caused by fluctuating ( ie going from high to low) CO2.
I have 6 tanks, various algae at various time, but BBA in only 2, and these are the only 2 that I have used CO2 in.
One was. 50l with DIY , BBA started from almost day 1. Stopped the co2 months ago but BBA still going strong.
The other is my 350l tank. I tried DIY in this, had no effect, no BBA probably because I never managed to get levels very high. But when I changed to compressed co2 it was fine until the reactor jammed, effectively stopped injecting for a couple of days and BBA was triggered.
And the trouble with BBA is that once triggered it does not go away even if you correct everything.
Why does fluctuating CO2 cause algae? Hopefully Ceg will give you a proper answer, but my guess is that algae are caused by lots of things, mainly light, but also promoted by waste products. When plants are adapted to a particular light level and co2 availability, and then the co2 level suddenly drops they struggle and leach waste products, that triggers the BBA.
I would advise against DIY co2. Compressed co2 is really quite easy to set up.


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## Ady34 (20 Jan 2014)

Hi MrMacey,
Spnl is on the correct train of thought here:


Spnl said:


> When plants are adapted to a particular light level and co2 availability, and then the co2 level suddenly drops they struggle and leach waste products, that triggers the BBA.


It isnt necessarily because of the fluctuating levels of c02, algae dont really care about lack of c02, but the effect the fluctuation has on the health of the plants is the issue. If c02 fluctuates/drops off then, presuming lighting intensity stays the same, the plants havnt the necessary food source available to carry on growing, and especially if the lighting is strong they fail, not only polluting the tank from their demise but not actively filtering and oxygenating also. This quickly provides the algae a feast and they can pretty much grow in any water. 
Like everything though it is a balance, and under low lighting conditions you do have more room for error and a gradual drop off may not result in algae as the plants are not under huge pressure to perform and can adapt. This is a drawback of the yeast type systems as they are quite inconsistent in their c02 delivery, which if not managed with low lighting results in algae.
It all depends on how much lighting you are using, and whether you can easily reduce intensity along with the drop in c02 availability.
Cheerio,
Ady.


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## MrMacey (20 Jan 2014)

Thanks for the info! Never knew there was that much CO2 in the atmosphere to be honest! This may be another stupid question, how do aquatic plants in their natural habitat stand a chance? The lighting from the sun is superior to any of our lighting systems and correct me if I'm wrong (again) I can't imagine that the plants have the 400ppm available to them under the water because as you said, the fauna wouldn't be able to survive?


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## kirk (20 Jan 2014)

No but Theres a lot of algae in the summer it takes over lakes killing millions of fish in lakes. Just using the river as an example, there's not a lot on the beds in slow rivers it all reeds and lillies. So most plants poke them selves out of the water bingo as much co2 as they'd like.  Faster flowing rivers tend to have more oxygenating weed  running thick along the bed. I imagine plenty of co2 is in faster flowing rivers  (white water)  or near weirs.  Saying that it almost makes no sense as in the hot weather fish head for outlets and weirs as oxygen is higher there.   sorry I haven't answered your question I just thought I'd add to the interesting convo.


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## Ady34 (21 Jan 2014)

MrMacey said:


> Thanks for the info! Never knew there was that much CO2 in the atmosphere to be honest! This may be another stupid question, how do aquatic plants in their natural habitat stand a chance? The lighting from the sun is superior to any of our lighting systems and correct me if I'm wrong (again) I can't imagine that the plants have the 400ppm available to them under the water because as you said, the fauna wouldn't be able to survive?


 
yep the sun is bright, but also can be shaded by cloud cover, algae or even the surrounding vegetation by the river/stream. The sun rises and sets also reducing intensity throughout the day, only at full intensity for a relitively short period. Reflection/refraction of light during sunrises/sunsets and water surface movement makes it less intense underwater. Water itself can be tannin stained or have lots of waterbourne sediment which again reduces intensity.
Many plants we submerge all year round are exposed seasonally and grow easliy emersed, when submerged deep rooted plants feed from c02 reserves within the sediment which we cannot emulate in our closed systems. Longer stems grow towards the surface where c02 is more readily available. Other plants can sequester carbonates from the water and turn them into carbon for growth such as vallisinera sp.

Cheerio,
Ady.


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## parotet (21 Jan 2014)

Hi, look for 'rubisco' in the search engine of this forum... Plenty of interesting information about plant health, co2 fluctuating levels and associated problems. I am using more and more this searching option. Works great!


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## parotet (21 Jan 2014)

Check also this one:
Effect of fluctuating Light Levels on Plants & Algae | UK Aquatic Plant Society


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