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RE UV vs Polishing Filter (was Re: U V Sterilizers)

Lamp intensity and duration of exposure are both factors affecting the
amount of exposure.  For UV lamps to be effective against protozoa,
higher intensities or longer exposure times are needed than for smaller
organisms at a given intensity.  The difference between protozoa,
free-floating algae, and bacteria is substantial.  But the exposure
rates for any of these are not so high as to be impractical in aquarium
applications -- depending, of course on your pocketbook.  

See, for one example, http://www.aquanetics.com/uv-cons.htm for lamp
sizes and recommended water flow rates using Aquanetics products.  For
another, see http://www.emperoraquatics.com/aqusmartuv.html for Emperor
Aquatics Lamps.  Reportedly, suitable exposure intensities and
durations, not to mention repeated exposures due to recirculation of
the water, are possible and effective for many protozoa as well as
smaller organisms.

Compared to a diatom filter, the filter would not remove the smaller
organisms.  So an argument could be made that the UV Lamp handles all
three while the Vortex does not.

On the other hand, the Vortex is cheaper to maintain (diatoms are
cheaper than UV bulbs) and does not effect chelators and iron
availablility.  Conceivably, by breaking down chelators, a UV lamp
could make iron more readily available to attached algae even though it
kills off free-floating algae.  I have not done, nor read of any
comparative cases or studies on this matter -- it's just where the
logic seems to lead.

Anyone have some hard data on this?

If you read about UV, even from the sun, you'll find that it can be
pretty nasty stuff even for human cells much less euglenoids and the
other smaller creatures.   Of course exposures lethal to humans are
extrodinarlily high compared to those for protozoa.

Scott Hieber

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