09 Equipment: Filters
Description
This article is from the Beginning Fishkeeping FAQ, by Thomas Narten with numerous contributions by others.
09 Equipment: Filters
There are three types of filtration: biological, mechanical and
chemical. Biological filtration decomposes the toxic ammonia that fish
produce as waste products. All fish tanks MUST have biological
filtration; biological filtration is the cheapest, most efficient and
most stable way to breakdown toxic ammonia. Mechanical filtration
traps such particles as plant leaves, uneaten food, etc. (collectively
known as mulm), allowing them to be removed from the tank before they
decompose into ammonia. Chemical filtration (e.g., activated carbon,
zeolite, etc.) can remove (under limited circumstances) such
substances as ammonia, heavy metals, dissolved organics, etc. through
chemistry (e.g., ``adsorbtion'' or ``ion-exchange resins''). Chemical
filtration is mostly useful for dealing with short-term problems, such
as removing medications after they've served their purpose, or
purifying tap water before it goes into a tank. A healthy tank DOES
NOT require the use of chemical filters such as activated carbon.
One point about filtration cannot be made enough. ALL FISH TANKS MUST
HAVE BIOLOGICAL FILTRATION. Although chemical filtration can remove
ammonia under limited circumstances, it are NOT a general solution.
Typical filters perform some or all of the three filtration types in
series. Mechanical filtration (if present) usually comes first (where
it is called a ``pre-filter''), trapping particles that might clog
remaining stages. Biological usually comes next, followed by the
chemical filtration section (if present). Whether or not chemical
filtration is useful (or even helpful) depends on who you talk to. It
can be useful for removing fish medicines after their effectiveness
has ended (partial water changes do the same thing though). They can
also remove trace elements necessary for plant growth (with obvious
results). Unless you have a good reason to believe that your
circumstances require chemical filtration, avoid it.
Filters are not maintenance-free. For example, if debris is allowed to
accumulate in a mechanical filter, it decomposes into ammonia,
negating its primary purpose. Likewise, a biological filter's
effectiveness diminishes as it becomes clogged. Biological filtration
requires water movement across a large surface area on which bacteria
have attached (e.g., floss or gravel). The less surface area
available, the less effective the filter. UGFs are cleaned by
regularly vacuuming the gravel (e.g. while doing partial water
changes). Canister and power filters are cleaned by removing the media
and gently squeezing it in a bucket of used tank water (tap water may
contain bacteria-killing chlorine).
There is no magic formula for what size filter one needs. Consult with
specific manufacturer's ratings and be conservative. You can't have
too much filtering (though you can have too much water movement), so
err on the side of overfiltering. Filters are discussed in more detail
in a separate FILTER FAQ.
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