07 Undergravel Filters
Description
This article is from the Aquaria: Filters FAQ, by Bruce Hallman.
07 Undergravel Filters
Fish stores commonly sell undergravel filters (UGF's) to beginners in
``aquarium kits'' because they are cheap, and they work (for a while).
UGF's work by slowly passing water through the bottom gravel, which
sits on top of a perforated plate. The water can be pumped with an air
lift, with bubbles air lifting the water in a vertical tube attached
to the filter plate. Also, some people prefer the increased water flow
achieved with submersible pumps, called powerheads, attached to the
same lift tubes.
UGF's make good biological filters, because the slow flow of water
through the gravel fosters large colonies of beneficial bacteria which
neutralize toxic ammonia. The hitch is, that UGF's are awful
mechanical filters. Fish waste gets pulled out of sight into the
gravel. Before you know it, the gravel clogs up. You then have a big
mess and a health risk to your fish!
A partial solution to this dilemma is to run the powerhead in reverse,
sending water up through the gravel. This technique is known as
Reverse-flow Undergravel Filtration (RUGF); conversion kits or special
powerheads can be purchased to accomplish this. The intake of the
powerhead is covered with a porous sponge which serves to "prefilter"
out some of the waste that can clog the gravel. In actually practice,
this helps, but is only a partial solution.
If you choose to use an UGF/RUGF, you must regularly vacuum your
gravel. Fish stores sell siphon hoses with a ``wide mouth gravel
vacuum tube'' attachment that ``washes'' the gravel during your
regular water changes. IF you clean your gravel regularly, and
maintain a regular and frequent partial water routine, UGF's and
RUGF's are an economical and effective aquarium filter in freshwater
aquariums, and in lightly stocked saltwater fish-only aquariums.
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