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Re: Bactweria/filter removal

On Thu, 20 Apr 2000, Tom Barr wrote:

> 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.

> Would the plants be able to get it(25/75 split) as easy as the bacteria or
> what factors may cause the bacteria or the plants to gain the upper hand?
> Substrate physical nature come to mind and cycling status of the tank, flow
> rates through the substrate etc. ..........
> What happens when you really disturb your substrate? Crash city
> ............even if the plants and everything else is well maintained.

I haven't run across original support for the 25/75 split but I gave it a
little thought when you first brought it up.  I guess this would have been
placed better there.  I think the nitrogen concentration in hyroponic
solutions is higher than we usually want in our aquariums.  If you try
supplying all of the nitrogen to the plants as ammonia then you have a
pretty high ammonia concentration in the solution.  Guess what...high
concentrations of ammonia are toxic to plants.  Probably the 25/75 mix
provides the highest concentration of ammonia they can put into a
hydroponic mix without seeing growth reductions due to toxicity effects.

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

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 then the tank provides between the water and the plant surfaces.
This intimate contact favors the bacteria.

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.  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.

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.

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.

Roger Miller