"Elaine T" wrote in message
om...
George wrote:
"Sean Dinh" wrote in message
...

TT and nitrate reduction...
http://tinyurl.com/4hlhx


10 ppm is not acceptable in reef aquariums, and I strongly suspect it does
little good in large freshwater systems (such as garden ponds) with
no/inadequate plants to remove it. Hence, the algae blooms. In a sand bed
that uses a Jaubert plenum, a porous plenum is constructed beneath the bed
with a void space below the bed that is filled with water, anaerobic bacteria
form in the bottom depths of the substrate and in the water below. As
anaerobic bacteria cultivate, they remove nitrates. Anaerobic action produces
a fair amount of heat. The heat warms the water layer below the gravel. The
warmer water flows upwards, displacing cooler water above the gravel. This
action moves water through the plenum at very slow rates. The slow movement
of water through the gravel helps to prevent dangerous hydrogen-sulfide gases
from forming in the plenum. The deep gravel bed also provides a home for
burrowing motile invertebrates which feed on solid organic mulm and detritus.
The idea here is to move away from systems that required heavy maintenance to
prevent nitraqtes from getting too high. Trickle filters work great in
removing nitrogen compounds over a limited time period before they must be
maintained (i.e., cleaning pre-filters, etc). Sand beds with a Jaubert
plenum usually never have to be cleaned because, if it is properly
constructed, there is no build up.

http://www.practicalfishkeeping.co.u...?article_id=21
Jaubert plenums have been tried in large FW planted tanks shortly after they
became popular in sal****er. It is much harder to get a population of
denitrifying bacteria in FW that does not include sulfur reducing bacteria and
generally attempts at denitrification in FW crash and burn. Sulfur reducing
bacteria establish in the plenum, poison the water, and fish start showing all
sorts of bizarre diseases in what otherwise seems to be a healthy system.

--
__ Elaine T __
__' http://eethomp.com/fish.html '__

Do you have a link to any papers on this? I found a web site this evening that
describes the set up and it seems to suggest that it works very well, at least
in freshwater aquariums. It also recommended to use 2-3 mm diameter gravel
instead of sand. Since we are talking about a lot more water, I am considering
using even larger gravel (probably something slightly smaller than peah gravel).
I've also read elsewhere that fears of crashing and burning are unfounded if it
is done properly. Of course, like any experiment, I'll have to monitor it.
Sulphur-reducing bacteria could become a problem if the substrate becomes
completely anoxic. But most sulpur-reducing bacteria are anoxic. The idea of
using a live gravel bed in a garden pond must take into considerations all of
the needs of the bateria that will live there. De-nitrifying bacteria are
anoxic, while ammonia reducing and nitrite-reducing bacteria are aerobic. The
idea is to get all three types growing in the same substrate. So can we expect
these three bacteria to live viably together? The answer is yes, IF oxygentated
water is induced to flow just above the gravel (parallel to it), which will
induce flow/exchange within the gravel, but at a low rate. I suspect that my
hogs (fish) will also root around in it enough looking for food that it will get
enough oxygenation. But I plan to come up with a way to create the current flow
a few inches above the gravel. I already have a very thin layer of gravel on
the bottom (I had extra gravel when I built my biofilter, and I wanted to add a
little color to the bottom of the pond), and they do root around in what I
already have there. But I will certainly take your advice at heart before I
make any final decisions. Thanks for the advice. Oh, and after reading that
article, and your advice, I will probably lose the plenum and just build the
substrate right on the bottom. Here is the link to the site I found:

http://www.athiel.com/lib/lg-fw.html

Here is another one about gravel filtration (as opposed to undergravel
filtration):

http://www.athiel.com/lib/ugfilterarticle.htm

Just read the part about gravel filtration.