Freshwater

64
Part I: Aquarium Basics
filtration and are inadequate for use in large tanks. One other problem with a
sponge filter is that it makes your aquarium look kind of like the junk shelf
underneath your kitchen sink, because it takes up room inside of the aquarium.
One good use for sponge filters is to quickly build up a biological bacteria
medium for new aquariums.
Corner filters (submersible filters)
Corner filters function primarily as mechanical filters but also provide biological
and chemical filtration. This is one of the oldest filtration systems known
to the aquarium hobby. Corner filters were originally designed for the small
aquariums that were the staple of aquarium-keeping years and years ago.
Generally, the original clear plastic filter was shaped like a small square box
and contained an airstone that pushed water through a layer of charcoal and
floss with the help of an air pump.
Fortunately, corner filters have really come a long way in the last decade. The
newer corner filters are much quieter; many come with swiveling spouts to
change flow direction and water flow adjusters to change the power of the
water flow. You can also find corner filters that have a clogging indicator that
will show you when the filter media needs to be maintained.
The old corner filters rested on the gravel bed inside the tank (if you could
manage to keep it from floating all over creation and back by weighting it
down with small pebbles or gravel). There are corner filters today that can
hang vertically and horizontally on the glass walls. The downside is that they
still take up room in the tank and can only be hidden using strategic placement
of plants and other aquarium decorations.
Power filters
Power filters are cool because you can use them for mechanical, chemical,
and biological filtration. A power filter runs on electricity (with an internal
motor so a pump isn’t needed) and usually hangs on the outside of the aquarium.
Power filters are box-shaped and come in a variety of sizes to meet the
needs of different-sized tanks (see Figure 6-1). These units usually have one
or two slots on the inside of the unit that hold removable fiber-coated filter
pads. The inside of these pads usually contain charcoal.