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RE: [APD] An observation
George Booth, in a message dated Sat, 27 Feb 1999, wrote:
>The problem is that the concept was grossly oversimplified. The assumption
>is that nitrifying bacteria are only in the filter - "no filter, no
>nitrifying bacteria". This is not correct.
>Nitrifying bacteria occur everywhere in an aquarium; on the gravel, on the
>glass sides, on equipment, on plant leaves, even in the water. Biological
>filters are useful in that the biomedia provides for a higher concentration
>per volume of bacteria.
>Dr. Alfred Gianascol, in "Water Chemistry in Closed System Aquariums"
>(1987), demonstrated that in a typical aquarium [without plants], the
>actual filter only provided about 15% of the total nitrification. The
>biofilm on the glass and gravel provided the rest.
>So, you can safely assume that there are in fact huge numbers of nitrifying
>bacteria in even the most densely planted tank and that they will happily
>convert any ammonia/ammonium that drifts their way into nitrate. They DO
>compete with the plants for nitrogen and WILL generate nitrate.
(Gotta love those archives!)
I would guess, based on Dr. Gianascol's findings, that in a filterless tank the
rest of the aquarium simply grows a slightly thicker biofilm in order to keep
So I have to wonder if Tom's experience with filtered vs. unfiltered tanks is
due to something other than biological filtration. Perhaps mechanical
filtration catches some of the algae spores? Perhaps activated carbon is
reducing DOC levels? (On filtered tanks, I've sometimes noticed that a fresh
batch of carbon can really set back a bloom.)
I can certainly believe that certain types of filters can help avoid algae
blooms in some situations. I'm just not seeing how it can be due to biological
- Jim Seidman
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