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Re: Aquatic Plants Digest V3 #526

Kudzu wrote:

> I read somewhere that Magnum filters don't have bacteria hosting material in
> them because they prefer to let the bacteria setup in the tank.

As I understand it, they think their filters are best used for mechanical
filtration, rather than biological filtration.  I have a Magnum 350 and
use it for polishing but it could be used for biological filtering by
placing any high-surface area medium into the activated carbon chamber. 
> My first thought
> was OK the bacteria sets up housekeeping  in the gravel in the tank. Then I got
> to thinking if that is correct then why would we even need filters? (I am
> thinking of ammonia only, not mechanical filtering) Why wouldn't the bacteria
> just set up in the gravel and do its job. The more I pondered on this I kept
> coming back to the common element here seems to be water flow over the bacteria.
> UGF flows water over the gravel and Filters threw the media.

Actually, the nitrifying bacteria set up shop on any surface and are found
free-floating in the water.  Gravel is not required.  In fact, plant leaf
surfaces are colonized by the bacteria and that causes me to think that
in a mature tank there is little foliar uptake of ammonia by plants - the 
bacteria are likely to get it first.  The plant hosting the bacteria would 
get first dibs on the nitrate produced by the bacteria.

The form of many submersed plants like cabomba, mayaca, and so on seems to
maximize their surface area (probably as a means of maximizing CO2 uptake
under low CO2 conditions) and that form also makes them great hosts for
large populations of nitrifying bacteria. 

> Do the bacteria need the water flow for oxygenation or for to bring their food
> (ammonia) to them?

In a standard sort of filter, they need it for both reasons.

> Also Assuming that water flow is the important factor here in theory wouldn't a
> power head or something else that caused a steady flow over gravel on the bottom
> of the tank do the same thing?

The idea with a UGF is to get flow through the substrate so that the
bacteria can colonize all of the surfaces in the substrate.  Flow over the
surface of the substrate only supplies oxygen and ammonia to the top
surface of the substrate.  Circulation in the open water does provide a
continuous flow of oxygen and nutrients to the bacteria colonizing other
surfaces in the tank and I treat it as an important part of the setup in
my unfiltered tanks. 

Rhonda Wilson provides a wonderful website on natural aquariums at


Anyone who has an interest in natural or otherwise low-tech planted tanks
should see her site.  My unfiltered tanks differ from her's mostly because
I provide more circulation than she does. 

Roger Miller