co2 Flux question


Guru Class Expert
Jun 5, 2005
Dallas, TX
I posted this in the forum but didnt get any responses.

Been reading quite a bit lately that co2 fluctuations can/will cause algae.

So, my question:

Since plants max out at uptake of 30ppm co2, is it still considered a bad flux to have co2 flow between, as example, 30 and 50 over a short period of time? Or is the "bad flux" mainly saying dont let co2 flux much under or stratling 30ppm?

Ian H

Guru Class Expert
Jan 24, 2005
Shipley, West Yorkshire, UK
Re: co2 Flux question

I don't think that variations above 30ppm would cause any negatives except being wasteful on CO2 and potentially harmful to the livestock. It is important that you try to keep the CO2 levels from changing too quickly. If you put a quick,heavy burst of CO2 into your tank the creatures will become distressed very quickly.

CO2 is only a small part in the sucessful growing of algae free,healthy plants. An important part I agree, but not the whole story. It's a perpetual balancing act of CO2 input/lighting/nutrient dosing/nutrient uptake/plant types and stocking levels. If you get out of balance in any one of these areas you are likely to have some problem emerge.



Prolific Poster
Apr 1, 2005
Re: co2 Flux question

CO2 should be thought of as a nutrient (it, carbon, is). We think of nitrogen as a quickly used nutrient, and it is. In a scientific journal article, carbon was part of the Redfield Ratio, and drawing a highly unscientific and very loose generalization, C is used roughly 10x faster than N. I'm thinking the lighting referred to would be sunlight, so obviously, this will vary in the aquaria, as light acts as a catalyst for plant growth given proper (unlimited) nutrients. This also does not consider the plant or animal biomass, along with other variables. Don't go 'round quoting me on that.

Our goal is to keep it at the proper level, and to keep it stable. I'm thinking this is because it will off-gas to the atmosphere, and will become used via respiration of plants & fish. Like any algae would, it will rear its ugly head when nutrients become deficient. You may have all the other variables (N, P, K, traces, light, etc.) held constant, but when you alter the C variable (i.e, it becomes deficient), things are thrown out of balance and boom, algae.

Just my 2 cents, as scratched up as they may be. :)

Greg Watson

Staff member
Jan 23, 2005
United States
Re: co2 Flux question

Spar said:
IBeen reading quite a bit lately that co2 fluctuations can/will cause algae.

Not counting the "Redfield Ratio" above ... I'd agree in general with David and Ian above ...

In the hobby, we have a lot of "annecdotal" analyses that become part of our general practices ... I am quite confident that Ian hit the nail on the head when he brought the "range" aspect up - that above a certain unspecified range, wild CO2 fluctionations are unlikely to have any significant effect. And David also hit the nail on the head that we really should think of Carbon as a nutrient that we dose just like our macros and micros ...

Now if we think about Cabon as a Nutrient and then think about dosing it in a common sense manner like EI treats macro nutrients, then our goal should be to maximize our CO2 levels within a range that is not harmful to our livestock (gee, that sounds just like what Ian said) ... we essentially are dosing carbon ...

Now Tom often tells us that there really is nothing wrong with turning off the CO2 at night and turning it back on in the morning when the plants will be consuming the greatest portion of it ... Now if we make the assumption (like David brought up) that Carbon is consumed at a relatively aggressive uptake rate, this would actually make sense ...

And if we again tie that back to the EI philosophy of dosing to acheive a maximum within a range ... we shouldn't have any problems except when we run out and our plants have to work harder at finding other sources of carbon within the water column ...

And since I started this post with the observation that we have a lot of "annecdotal" analyses that become part of our hobby ... have you heard one of the latest anti-algae rumors running around? There are a few people that are advocating a Flourish Excel dosing supplement to our pressurized CO2 to add an additional source of Carbon to fight algae ...

So annecdotally, in the context of part of a CO2 swing including a bottoming out (i.e. running out of CO2), then yes, I suspect that there is a algae aspect to a CO2 swing, but I am quite confident that the context is in the bottoming out of the CO2 or running out of CO2 aspect ...

Gee ... in most cases, the only reason I know that my CO2 tank is empty is because all of a sudden I see algae growth ... then I know its time to change my CO2 tank ... there, that ***PROVES IT*** - CO2 swings cause algae ... I know it, I can prove it ... all I have to do is let my CO2 levels swing when my pressurized CO2 tank runs out and I get algae! There, we have proved it, CO2 swings cause algae !!!!

All jokes aside ... we have a lot of annecdotal things in the hobby that scientifically may not be valid, but when put into practice, often they teach us to perform certain tasks in a consistent manner ... and it is some other aspect of the consistent practice that is really what benefits our plants ...

So if you think about a lot of the things that you hear in the context of "best practices" they often work even though they may not be scientifically sound. Thus if you can keep your CO2 levels stable ... I suspect that the implication is that you will always have some level of CO2(ie carbon) available...

So I am also confident that stable CO2 levels are probably one of those good "best practices" kinds of things ...