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>On Thu, 20 Apr 2000, Tom Barr wrote:
Regarding removal of outside filtration:
>> But suppose the bacteria are then concentrated further in the substrate?
>Bacteria in the substrate will be significant if you're using UGF or RUGF.
>Otherwise, if you aren't actively circulating water in the substrate then
>the contact between the water and the surfaces in the substrate is so
>limited that it's not much of a factor.
Something doesn't jibe here. 
There is some flow through a gravel bed, like Amano's or my Flourite/turface
etc.   These have very high surface areas and no added flow. These are some
of the "best" substrates around and have no flow but due to the surface
area/grain size and ability to have water circulate well through them they
do a super job with or without a filter. The films can attach to these and
the internal surfaces also.  If a substrate has a good flow-- as these do
--why is it then not a factor? It is not much different than the water
column to a certain degree although it is less than a filter........ I still
wouldn't rule it out by any means.  Wouldn't a richer broth (from outside
filter removal) give you more bacteria even at the same old flow rates? Same
would apply to a filter would it not? Seems the same can be said for the
substrate here. 
    The flows through real tight or capped substrates will not be as good
and this will not be as big as a factor sure...... but most of the better
substrate materials seem to have an aerobic nature about them and this would
make a difference and be a factor for a larger population of bacteria. The
flow would come close to the water column some in these cases although still
allowing the plants to get the NH4+ easier than the bacteria. What about all
that mulm? It has always been a great planting additive for a new tank and
an old one. It builds up and keeps on building up and the tank seems to be
better balanced. What all is in that? Bacteria and inorganic matter I would
think. What about rockwool? Does water flow well through there? Again, lots
of surface area. There is a good flow but nothing like the filter or the
water column but dismissing it as not a factor is simplistic at best.   

I suppose a balance could be achieved were the NH4+ is added in very small
amounts in a balancing act by fish/critters or perhaps by a an inorganic
source(a long term stick comes to mind) were there would be only a very
minimal amount of bacteria but it will cover the gravel everywhere. The
plants can get more NH4+ than the bacteria in this case generally but are
there other bacteria that are indirectly associated with the N cycle? Some
don't need this flow as they get their O2 from the roots of plants? Would
that explain why the gravel being well disturbed might cause a crash?
Why do plant appear to "need the gravel" so much then if not for the
bacteria/bacterial cycles? Generally we do not mess the gravel up if ever
except for replanting. Do too much and you get a crash. If it is all
inorganic and no bacteria is better -or only a small amount- why does this
crashing happen? I may be blind here but what am I missing? Something seems
not quite right.

>In our aquariums the nitrogen concentration should be lower and the
>optimum ratio should be different.  Quite possibly, at low concentrations
>it is most efficient to supply 100% of the plants nitrogen demand with

What do you or anyone else think might be a good range here? Soil substrates
often have high amounts of ammonia don't they and these do well? What about
adding some time release source etc? Jobes? What is the threshold of
toxicity of NH4+ for submersed plants? 1 ppm in the column and what for the
soil? Is KNO3 the best thing we can add here? Add it at night for the
respiration cycle? In the soil or the water column? I would think the soil
IMO for NH4+. KNO3 is going to go where ever it wants pretty much being so
soluble or can it and/or NH4+ be bound up and released later like Fe?

>The relative size and surface density in the tank and the filter plays a
>role in whether plants or bacteria get the best shot at the ammonium.
>Normally the filter (or gravel bed) is a relatively small thing and
>there's a lot of surface area packed into it. 
 The tank is a relatively
>large thing with a substantial amount of open space and much less surface
>area.  The tank and the filter have the same flow-through rates, so the
>filter provides for much more contact between the water and the bacterial
>film than the tank provides between the water and the plant surfaces.
>This intimate contact favors the bacteria.

True. What about when the flows are less through the gravel beds than
through a filter? Favoring the plants with a slightly to moderate aerobic
gravel bed like flourite etc. and doing away with the filter? The plants
would be favored then without going to the extreme of ferreting out most of
the bacteria and allowing some N for the bacteria.

What about the plant roots where both the plants and bacteria are together?
The surface area of roots is very high compared to the leaves is it not?
Perhaps exceeding the filters themselves. O2 is brought down to the roots
also. It seems the favor is in the plants but the bacteria are so close and
all over the plant that they "sponge" off them for nutrients. Comments?

>Meandering along to other topics in this thread, it has been pointed out
>that bacteria will colonize surfaces in the tank.  On any exposed surface
>in an aquarium the bacteria will have to compete with algae and
>cyanophytes - they won't have the free reign that they do in the darkness
>of a filter.  Also most of us keep fish and snails that graze surfaces.
>Those critters are bacterial population control. 

And also algae. Many species of bacteria BTW live on Algae's surfaces. I
know you know that though! :) Ye old tadpole protein source as there is not
enough in algae alone for them to grow otherwise.

 We generally aren't
>going to get big populations of nitrifying bacteria growing on leaf
>surfaces because the bacteria get eaten.  In tanks where for one reason or
>another the biofilm does get out of hand it becomes visible and an
>aesthetic burden.  Then the ultimate competitor (the aquarist) steps in
>and cleans things up.

Algae comes to mind again and plants too. What about roots? No critter
cleans the roots.

>I'm not saying there will be no nitrifying bacteria in an unfiltered tank.
>I'm saying that in an unfiltered tank the competitive edge swings sharply
>toward the plants.  There may still be nitrifying bacteria but their
>overall effect will be much reduced.

I still think with a porous substrate this will not be the case. Try this
out then.............
Cap your substrate real good with super fine sand to slow the flow way down
and add what ever you want in there.
Try another tank with flourite/turface etc and see what happens to each.
Why would you think the turface tank would fair better? Or worse? Are you
saying that turface it is all inorganic in it's ability to grow plants here?
Why have any gravel at all or at least very little for the plant then? Would
this do better then? There's some hogwash here somewhere. Maybe on my part.

>And last, I wouldn't want anyone to think that removing a biological
>filter is going to revolutionize your tank.  I think that it's something
>you do if you're maintaining your aquarium primarily to keep plants.  It
>can improve plant growth and it can simplify maintenance but if you're
>thinking of taking biological filtration off your tank then you need to
>weigh the possible consequences.  On the up side you get less maintenance
>and possibly better plant growth; on the down side your fish can die. Over
>the years my attitude has shifted so that I now keep my tanks primarily
>for the plants, so the good consequences outweighed the bad ones.  As it
>turned out, my fish were just fine and they still are, but it might not
>work that way for you.

Tom Barr