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[APD] Re: theory behind algae control

An interesting question, and one I found myself pondering (once more) this
weekend.  One of my CO2 tanks ran out.  The first visible sign that it was no
longer running was an uptick in the variety and amount of algae in the tank. 
It caused me to think.

Non-technically speaking, there seem to be four things that go into algae control:

1) Redefining the problem.  Some people start out thinking that any visible
algae in an aquarium is a problem that needs to be controlled.  Algae problems
sometimes fade quietly away when the aquarist relaxes and accepts that some
algae can be present without being a problem.

2) Establishing conditions that limit the number of algae that can thrive. 
With maybe a few exceptions algae are specialists that survive only in a
narrow "window" of conditions.  Algae that can't survive under those
conditions disappear.  Many different windows seem to work, as long as the
window is small enough.

3) Maintaining stable conditions.  This goes hand-in-hand with number 2.  If
conditions in an aquarium vary then the "window" of conditions that your
aquarium provides gets bigger.  This is most obvious in new tanks, when you
make any big change in a tank and when things happen beyond your control
(i.e., CO2 tank runs out).

4) Tuning the algivore population.  You need to have algivores that eat the
algae that survive in the window of conditions that your aquarium provides. 
Some of those algivores are macroscopic, some are likely to be microscopic. 
There may even be a phage or two involved.

A lot of the technical discussion over algae control relates to #2; just how
do you set up a good window of conditions?  There seem to be quite a few ways
of doing it.  I'm not sure the differences are as significant as the
similarities.  The main similarity is this; the plants you chose to grow are
all healthy under the conditions you provide.

Different algae-control methods have claimed followers at one time or another.
 Even methods that didn't make much sense have claimed successes.  I think the
main reason for that is in #3.  When an aquarist adopts a method and follows
it faithfully for a reasonable period of time they get stability.  If those
conditions also support good plant growth then they will continue with those
stable conditions.  It's like magic.  Or something.  

The idea of adding nutrients to somehow starve algae is an odd one.  That
approach is an all-out attempt to kill algae with kindness.  Still, it works
for some.  More generally we need to fertilize our tanks just like we
fertilize our gardens or our houseplants.  Give the plants what they need but
never give too much.

Roger Miller

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