[APD] The why of the Barr method

[Jeff Ludwig <jeff at rockytop_net>]

Now that everyone is discussing methods and on the defensive about the 
Barr method, I'll throw this one out there (I am NOT saying the Barr 
method or any other method does/does not work, I just want to dig a 
little deeper):

Why does the Barr method work?

I mean, we are also providing algae with all of the nutrients it needs, 
why doesn't it grow with the plants?  Tom has ruled out nutrient 
limitation as the technique clearly doesn't rely on this.  I have also 
seen several posts citing works that show how algae are much more 
competitive and able to utilize nutrients at low concentrations than 
plants.  So the plants aren't out-competing algae for nutrients...

The large water changes rule out alleopathy.  Based on Walstad's work 
it would seem you would need to not change water for months to see the 
effect of alleopathic chemicals, and even then these chemicals have 
their skeptics, particularly with alleopathic chemicals being released 
into the water column  (as opposed to soils).

Redox potential?  If this were at work injecting pure O2 or using ozone 
should also work, which it does not from what I've read (also see the 
old Barley Straw threads for discussion of this).  So what mysterious 
forces do plants growing well exert on a system to melt algae away (or 
at least stop its spread)?  Why does good plant growth inhibit algae, 
knowing the three reasons above are probably not it?

Fertile substrates (of which Amano is a huge fan AFAIK) and the 
standard PMDD method work by nutrient sequestering (keep macros in 
substrate) and nutrient limitation (which should not work according to 
studies performed with algae if those are correct).  Amano also uses a 
_ton_ of algae eaters, 1-2 C. japonica per liter, 1 otto cat per gallon 
(see http://www.vectrapoint.com), is this the secret?  Good plant 
growth and even better algae control via critters?

Some food for thought,
Jeff Ludwig
Elkton, MD

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