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Re: Overfiltered

I wrote:

>No matter how much volume (or area) your bio-filter has, you will NEVER
>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.

Peter Aitken disagreed:

"I am fairly sure that this is not true. Like other living organisms
can adjust to food availability by altering their intake and metabolism. A
fixed population of bacteria could survive just fine on X amount of
nutrients, and if the nutrients suddenly increased to 5X they would increase
their nutrient utilization to use the increased food supply (assuing
sufficient O2 etc)."

I'd love to see the basis for your doubt, and the research upon which you
base your feeling that some perceived over-population of bacteria are
lurking inside a bio-filter, existing on meager rations, just waiting for
their dinner call to turn up the heat, so to speak. Do you know of any
population density studies which have been conducted which back up this

I'm not doubting that bacterial metabolism rates can be adjusted based upon
conditions, but I do doubt that we should run out and remove the biological
media from out filters due to a fear that they are competing for nutrients
with our plants. Plants and bacteria work in concert, and that score has
been evolving for billions of years. I doubt that we should fear the
competition which exists as part of the natural processes which are
occurring in our tanks.

In Spotte, "Seawater Aquariums", there is a rather detailed account of the
factors affecting bacterial populations in slime films. And before anyone
jumps to the conclusion that this is not applicable to freshwater
environments, the research cited by Spotte was conducted both in marine and
freshwater systems. Bacterial action within slime layers can be affected
both by oxygen diffusion rates and by nutrient limitation. If the bacteria
in the deeper layers suffer from oxygen deprivation they die and slough off
the substrate. In the same fashion, if there isn't enough food for them to
maintain their metabolic processes, they fail to reproduce, and eventually
die. The sites used for bacterial attachment are recycled in a fairly short
period of time - "The life of a biological film is short. It matures
quickly, is sloughed off, and a new one forms in a matter of days.
Heukelekian and Crosby (1956) estimated that most wastewater films broke
apart regularly about every 14 days."

Spotte also states that "in the open sea, the role of heterotrophic bacteria
in the degradation of organic compounds far exceeds that of algae". I find
it hard to believe that the situation would be any different in a freshwater
environment. Nor do I think that "higher plants" would be any more effective
or efficient than algae in this regard. Both bacteria AND plants have a role
to play in keeping our systems healthy.

A heavily planted tank with a light to moderate fish load certainly depends
less on the presence of a large "traditional" biological filter than a fish
only tank, but the same processes occur in both. I doubt anyone is efficient
enough with their maintenance regime to prevent the formation of bacterial
slime formation within the aquarium as a whole or their filter in
particular, and I doubt that it makes very little difference (in a negative
way) that we allow/encourage bacteria to colonize and inhabit our filters. I
do doubt that a healthy aquarium can be maintained for any period of time
WITHOUT the activity of bacteria somewhere in the system.

The "traditional" ideas of sizing filters rely on an estimation of the
surface area available within and upon the media for colonization of
bacterial films. With limited nutrient availability (such as would exist in
a very lightly stocked system), there is a practical  upper limit on the
size of the bacterial population. The density of the bacterial population is
not going to exceed this limit merely because there is more surface area
available for colonization. In a heavily planted, lightly stocked aquarium,
sufficient surface area for the required number of bacteria might easily
exist within the body of the aquarium itself, without the need for a large
external bio-filter. But the mere presence of this excess capacity does not
mean that all this excess area is going to be occupied by billions of
"extra" bacteria, patiently waiting their turn at the dinner table.

James Purchase