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[APD] RE: Why algae does not grow

> Date: Fri, 1 Apr 2005 07:38:32 -0800
> From: Liz Wilhite <satirica at gmail_com>
> Subject: [APD] why doesn't algae grow?
> To: aquatic plants digest <aquatic-plants at actwin_com>
> Last night I got hit with a question I couldn't answer: why doesn't algae 
> grow in my tanks. I had a brief problem with algae -- some hair and BBA. 
> Hair algae cleared up when I dosed more and BBA was suddenly not in the
> one day about a month after increasing the CO2 content slightly. It
> come back. I credit Tom Barr with both the plant growth and lack of algae.
>  What made the question tough to answer is that the answer to the
> is clearly not "good plant growth". Yes, there is good plant growth, but 
> given that there are sufficient nutrients, light, CO2, etc. then why is 
> there also nice algae growth? What is it that is stopping the algae from 
> growing? Is allelopathy at work? Or is there something about the
> that give rise to good plant growth that make for a hostile environment
> algae? And if so, what doesn't the algae like?
> -- 
> Liz
Hi, Liz
On a  more serious note, I think it is a very poor assumption to assume
Allelopathy involves chemical warfare, what are the odds that all 300 or
species of aquatic plants we keep have the same chemical and the same
effect on algae?
Many chemicals are decomposed rapidly with UV sterilizers, easily removed
with activated carbon(which is used as a control in ecology studies on
How does a plant know how big their aquatic environment is? Why make
something if it will be washed away? Suppose the plant lives in a
unidirectional stream? What then?

Some folks have suggested very active allelopathic chemicals, only a tiny
amount needed or surface based but none have ever been found and no
allelopathic effects have ever been shown to occur in any wetland/lake or
stream to date. Again, what are the odds all plants have this? Many plants
are amphibious, so they really don't care if they have some algae for a
month or two, root mediated allelopathy is likely a more concern but the
algae we dislike do not have true roots, some marine and a few FW types
have something similar but these are far more plant like than the smaller
They also possess much stronger alleopathic impacts on epiphytes that may
grow on them than any plant. 

If you grind up a plant and add the juice in high
concentrations.........well.........that's not the same as a live plant,
nor the same concentration. If I spit enough salivia, I could say the same
Epiphytic algae that grow on plants have been around longer than the
plants, while plant might produce allelopathic chemicals, many algae can
produce counter chemicals to still attach and grow. Sort of an arms race.

I think where folks have the biggest problem with understanding why algae
does not grow when plants do is that the algae are in a completely
different ecological niche.

Surface/area ratios are totally different, uptake kinetics are totally
different, impact of NH4 presence is totally different.
While both Mice and Elephants are both herbivores, few would say they
compete on the same level. 
Aklgae are single to many celled, but nothing compared to a plant. Plants
are often 10^6 to 10^9th more biomass. 

Algae live how long? I mean=>each cell?
Maybe a month for many species we have issues with.
How long do plants live? Much much longer.

So if the algae stop growing, they eventually die off.
The plants remain. 

If you focus on the plant's needs, then the algae no longer grow.
We I see algae, it means there is something not allowing the plants to
grow, the algae are bioindicators thjat tell the environmental conditions.
I generally do not even need to know anything other than the species of
algae to help someone solve their algae issue.

Plants have a wide range of environmental tolerances, algae are fairly
narrow and very seasonal.

Many lakes in FL are choked with weeds, very little algae.
In our tanks, we remove the algae as well, add herbivores, add nutrients in
good non limiting levels.

We select for good plant growth(the original goal), not algae.

Tom Barr

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