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RE: Filtration's importance in plant tanks

Dave "Clueless" Gomberg asked about filtration's usefulness in a number of

>In a tank with lots of plants and
>1.  no animals, is filtration useful?
>2.  very few animals, is filtration useful?
>3.  moderate animals, is filtration useful?
>4.  In case 3, what role does filtration play?  What objectives does it
>accomplish?  What bad would happen if you omitted it?

Filtration, in the sense that most commercially available units work,
involves removing or modifying something which is perceived as "bad" from
the water. In the case of particulate material, it is either held in some
framework (sponge) until it is either physically removed from the system or
acted upon by bacteria and broken down into it's constituent minerals.
Either way, it's gone. In the case of dissolved substances, they are either
adsorbed onto other materials (carbon) or consumed by bacterial and
converted into less toxic substances (ammonia-nitrite-nitrate). How _much_
filtration capacity is a function both of the bio-load being serviced and
your own paranoia. No matter how much surface area is available for
colonization by bacteria, the number of bacteria is not going to exceed the
available food supply. I don't know if a bacterium is any better at grabbing
an ammonium ion out of the water column than a plant is, and I'd be
interested in hearing of any studies done to determine this.

A by-product of most filter systems is circulation - and this is beneficial
in tanks with animals and in plant tanks without animals. Water has a
tendancy to "stick" to surfaces. Without some form of mechanical movement of
the water, the layer of water in direct contact with the plants could become
oversaturated with waste products from the plants themselves. Circulation
will shear off this layer, replacing it with fresh water, and fresh
nutrients. In nature, most plants experience a lot more water movement than
you will find in a typical aquarium.

Running a low-bioload plant tank without filtration is certainly possible.
But some method of water circulation should always be included (powerhead),
in my opinion anyway. As the number of fish increases, and thus the bioload
in the tank, the importance of supplemental filtration capacity increases.
Its a balancing act that would be different for every tank. Having a filer
on a tank means that if something happened to the plants, the bacteria
attached to the biological filter media in the filter could multiply to take
up the slack and your fish wouldn't suffer. I don't know _anybody_ who feeds
their fish _lightly_. Most aquariums are eutrophic and a supplemental filter
is a cheap insurance policy.

Oh, and by the way - I'd never have thought you "clueless". <g>

James Purchase