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RE: "overfiltered"

Jared Weinberger gave some good advice regarding selection of a canister
filter but made one commnent which is just a tad overstated:

> There have been a couple of recent threads here on the Plant List
> about how
> much biofiltration is really needed in a planted tank, with the view that
> many of us may be "overfiltered", growing more bacteria than
> necessary that
> divert ammonia from our plants.

No matter how much volume (or area) your bio-filter has, you will NEVER have
more bacteria in it than is necessary for the amount of ammonia and other
waste products being pumped through it. Bacteria, like all living things,
require food and without it they will not reproduce and eventually their
numbers will stabilize at a point where each bacterium is able to get only
sufficient food for its needs.

Some people pre-condition their bio-filters using ammonia - in this way you
could conceivably have a huge population of bacteria in the filter, capable
of handling a correspondingly large input of ammonia on a regular basis.
When such a filter is introduced into a new tank with a low fish load (and
correspondingly low ammonia production level), the excess bacteria merely
die off until the population level is in equilibrium with the amount of
waste products being produced by your fish on a daily basis.

Should you later increase the fish load, the amount of ammonia flowing
through the filter will increase, causing the bacteria to multiply to the
point where their numbers are sufficient to handle the increased load. This
usually takes a little while - there is a time lag of perhaps a week for an
active, healthy bio-filter to grow to sufficient size to handle the new
levels of ammonia production. This is the main reason why it is important to
adjust your fish population slowly - allowing sufficient time for your
bio-filter to grow with the load.

People who advocate running "filter-less" tanks are not actually doing away
with the bio-filtration. Bacterial films exist on ALL surfaces within an
aquarium. In a tank that is heavily planted and has a small fish load, it is
quite possible for sufficient bacteria to grow within the tank itself to
handle the waste produced by the fish without having to provide for the
"artificial living space" for the bacteria inside of a canister filter (or
other such device). Also, the more plants that there are, in relation to the
number of fish (and their waste products), makes a heavily planted tank less
dependent upon the bacteria to deal with ammonia, as the plants can do the
same thing (plants are usually prettier than bacterial films too!). But I
doubt that ANY amount of plants can entirely do away with at least SOME
bacterial help.

Doing away with the bio-filtration capability afforded by a canister (or
other) filter assumes a couple of things - actively growing, healthy plants
in the tank (not those choked by algae); good water circulation, sufficient
to get the waste produced by the fish in good contact with the leaves of the
plants so that it can be absorbed; good maintenance practices so that you
don't over tax the system's capacity through neglect or over feeding or over

James Purchase