# High light require CO2 or algae will grow- WHY



## lobsterbib (Nov 7, 2011)

I keep reading how if you have moderate to high light, you need steady/reliable (ie NOT DIY) CO2 or you get algal growth.

What is the reason behind this?

CO2 is supplying growth substrate to the plant life in the tank. Aquarium plants and algae are both photosynthetic.

High light + low Co2= favors algae
High light + high/adequate CO2 = suppresses algae?

Is it that- without CO2 the plants can't photosyntheize as efficiently as algae?

this question has been bugging me!


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## willknowitall (Oct 3, 2010)

lobsterbib said:


> I keep reading how if you have moderate to high light, you need steady/reliable (ie NOT DIY) CO2 or you get algal growth.
> 
> What is the reason behind this?
> 
> ...


if your last question(speculation) was true why wouldnt algae still keep growing with high co2 even if the plants are getting what they need

my speculation is that the plants are adding and/or depleting something/s that the algae needs
and/or the carbonic acid is suppressing the algae and/ or spores
pretty wide speculation lol


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## plantbrain (Dec 15, 2003)

Why not just give the plants good steady light/CO2 and nutrients?
This is the goal, then algae is much less an issue.

The goal is to grow nice plants, focus there.


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## Byron (Aug 20, 2009)

lobsterbib said:


> I keep reading how if you have moderate to high light, you need steady/reliable (ie NOT DIY) CO2 or you get algal growth.
> 
> What is the reason behind this?
> 
> ...


Aquatic plants require sufficient light and 17 nutrients in order to photosynthesize; provided all this is available, plants will photosynthesize full out. This works to inhibit algae. The faster the plants grow, the more nutrients they use up, leaving none for algae; emergent and floating plants are especially very fast growing.

As soon as something is no longer sufficient, photosynthesis slows and may stop depending upon circumstances. CO2 is usually the first essential to lessen in natural or low-tech tanks. Plants then naturally slow down photosynthesis, using fewer of the other nutrients. Algae is quick to take advantage, as it can manage in much weaker light than plants, so any light that continues beyond the point at which the plants no longer have sufficient CO2 will only cause algae to increase.

This is the principle behind the "siesta" method of algae control. The mid-day period of no light allows CO2 to rebuild.

So the answer to your last question is yes. I have all natural setups, with minimal light. CO2 occurs solely from natural sources, primarily from the breakdown of organics in the substrate. But at some point it lessens to the point that the plants cannot photosynthesize fully. Once my tanks are established, I sometimes have to fiddle a bit with the light duration. If algae begins to increase, I reduce the light duration slightly, until it stops. Algae has previously increased in the summer, presumably due to the increase of natural daylight in the room (brighter and longer days); this past year I kept the blinds and drapes covering the windows (which face south and west) throughout the summer, and had no incident of algae. I have also had it begin to increase when the tubes are old and no longer emitting sufficient intensity. I believe that light is the governing factor in algae.

Byron.


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## plantbrain (Dec 15, 2003)

Sorry, but the using up of available nutrient for algae is a very easy test to falsify.

Example:










Tank has 15ppm of NO3 and 5 ppm of PO4 added 3x a week, and traces added about 5x a week at rather high non limiting levels, algae/specificaly periphyton, has about 3-5x lower range of N and P tolerance than any aquatic plant.

Likewise, a non CO2 tank, has about 10X less dosing, but similar ppm's at the end of the day.









You'd starve your plants long before you'd starve the algae.
This is true in non CO2 methods and Excel methods as well.
CO2 will increase the rates of growth about 10-20X.

I agree that light is a key player, as it drives CO2 demand and nutrient demand, and is about the only thing that algae/plants compete for. 

Still, I think simply focusing on the goal, which is growing plants........is the key here. Slower low energy non CO2 methods work well and generally use less light, and generally when done properly, have less algae. But the general methods are still the same, take care of the plants well, you have little algae issues.


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## Nix (Mar 7, 2006)

*Question for Tom*

Tom,

nothing to contribute to the thread, but I have questions about the tanks you showed above.
That first tank is stunningly beautiful with all those red plants. Please, have you perhapy discribed it anywhere else? I'm interested in the plants used, the lighting, the color of the lighting? I would love to hear about that tank (also how it looked later, when all had grown). It would be too nice, if you could answer those questions.

Thank you,
Nix


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## OVT (Nov 29, 2011)

Here is the journal on the first tank

PS: sorry to jump in before Tom, but I bet I sleep less


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## Nix (Mar 7, 2006)

Thank you very much, OVT!


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## galabar (Oct 19, 2011)

I think the answer is that no one knows why this is the case. Think "voodoo" until we have some conclusive scientific evidence.


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## Jimmyblues (Dec 16, 2010)

lobsterbib said:


> I keep reading how if you have moderate to high light, you need steady/reliable (ie NOT DIY) CO2 or you get algal growth.
> 
> What is the reason behind this?
> 
> ...


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## OVT (Nov 29, 2011)

If you find a way to make co2 explode please let me know.

via Droid DNA Tapatalk 2


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## freph (Apr 4, 2011)

OVT said:


> If you find a way to make co2 explode please let me know.
> 
> via Droid DNA Tapatalk 2


:hihi:

$60 a year for 4 tanks? Not bad, but I'll take my dual stage, timer controlled, laboratory precision metering valve tuned setup any day over some bottles filled with yeast, water and sugar.


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