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Re: UGFs -- Use Gravel for Filtration

Since they first became commerically available, I've been
hearing wonderful things about UGFs, mostly from vendors
but also from some accomplished aquarists.  And there's
less favorable stuff too, like, "They don't work."  They do
funciton, but how?

One of things you hear is that they only provide biological
filtration.  If that were true, they really would be as
useful and have as many practical applications as some
proponents urge (none that I've read on APD btw).  They'd
be like bioballs in a wet/dry in that they would rarely
(vurtually never) clog up under normal use.  You would
never need to clean the medium in a UGF if they only did

While the plate goes *under* the gravel, the filtering goes
on *in* the gravel.  The substrate *is* the filtration
medium.  They are so much *under* gravel filters and *use*
gravel filters.

The truth is gravel and and sand provide *excellent*
mechanical filtration, even with a mild water flow.  But
that's a problem if too much detritus builds up in the
substrate.  Using sand or gravel for mechanical filtering
is not new, novel, or rare.  I think sand filters for
aquarium use have been more commonly used in Europe but in
the USA, they have been used often in swimming pool
systems.  They are very effective, but you need to "blow"
them out or rinse them out if they filter a lot of
detritus.  How much is a lot?  I don't think very much.  As
Chico Marx said, "You gotta too much, that's a lot." ;-)
If the rate at which detritus reaches the substrate is very
low, then one can operate a UGF system for years -- in
principle, indifinitely.  That's in principle, in tanks
it's much shorter -- not all tanks just most tanks where
folks like to add fish.

As Robert H. pointed out, your plants can take care of the
Nitrogenous waste that you otherwise need lots of
biofiltration and water changes for.  And they're nicer to
look at took.

So forget filtratin for moment -- will a UGF keep the
subtrate fresh and vital for the long term, the way the
gentle currents from an undergravel heater may?  I think
rarely so -- the currents are almost always too strong to
avoid mechanical filtration and the compaction that often
occurs is more likely to foul the substrate than keep it
fresh and lovely.

I think the average amount of time that many if not most
first time buyers keeps an aquarium is about 6 month to a
year.  Then the person decides they've been neglecting it,
it's more work, or less interesting to them than they
thought it would be and they give up the hobby.  Some of us
get hooked.  But I think man/most(?) don't.  For those
folks, a UGF is a perfect filter -- it only has to work for
6 months - a year.  But if a lfs makes that kind of
recommendation, it's a cynical one at best.

Scott H.

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