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- To: "APD" <Aquatic-Plants at actwin_com>
- Subject: Re: Nitrates
- From: "Robert T Ricketts" <rtricketts at erols_com>
- Date: Wed, 27 Aug 2003 11:27:47 -0400
- Importance: Normal
"Jim Seidman" commented:
>I remember Diana Walstad
>discussing this in "Ecology of the Planted Aquarium." It's harder for
>plants to utilize nitrates than ammonia. To avoid using chemistry terms,
>think of ammonia as having more energy, which is why bacteria consume
>it. For the plants to utilize nitrate, they need to convert the nitrogen
>back to the ammonia form, which is energy-intensive. Many plants won't
>even make the enzyme to do this if there's ammonia present.
>So she actually warns against having too much biological filtration,
>saying this can lead to higher nitrate levels. In effect, the filter
>bacteria are competing with the plants for the ammonia. So you're
>converting a lot of ammonia into nitrates in the filter, and maybe the
>plants can't convert all of it back.
While I admire and respect all the massive research Ms. Waldstad did in
preparation for this book, I have grave reservations about some of her
conclusions and implications. I seriously doubt that these were rigorously
tested against the real world, and that was not in fact the aim of the work.
However, the popular acceptance and repetition of some of those conclusions
is pushing them into what I feel is dangerously close to aquarium mythology.
I run many planted tanks and many unplanted tanks, all of them having
filtration. I have many "spare" filters as I previously operated even more
tanks than I now run. Those spares tend to be operational on my tanks,
serving as back up and as preconditioned (inoculated) spares in case of need
for new setups. For decades it has been my practice to take one of the
preconditioned filters for a newly set tank and expect little or no
detectable unoxidized nitrogen-containing metabolites in "new" setups. This
works well when the canisters are from FO tanks, but not so well when they
have been housed on planted tanks. Asking several other hobbyists using
similar techniques got the same responses - filters from planted tanks have
nitrification bacteria at a well-inoculated level to start the process, but
insufficient to have no detectable unoxidized metabolites if taken for use
on new FO tanks.
From this I believe that exactly contrary to the project from the book,
biofilters do not successfully compete with plants, but rather the
opposite - plants quite successfully out-compete biofilters for available
nitrogen. The biofilters are left to scavenge only that available during
the dark cycle of the tank, or produced in excess of the plants' uptake.
The real-world experience does not support the book's projection and current
wide acceptance of the resulting myth.
Yes, it is correct that nitrate requires reduction inside the plant back to
ammonia for metabolism. The energy cost is nor massive for this, nor is
there reason for great concern. Do we not all add nitrogen in the form of
nitrate when a nitrogen supplement is needed? I don't know anyone bemoaning
the energy expenditure required by this.