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On Wed, 17 Oct 2001, Tom Barr wrote:
> Well if they are constant, you need to define what this constant level is.
> If it's low nutrient levels/high light then yes, BGA will make an appearance
> likely.
>      Natural successions in lentic systems are well documented.


There's a fairly well established ecological principle or theory that
states that the highest species diversity is found in moderately disturbed
systems.  Few species can establish themselves in frequently disturbed
systems, and very stable systems tend to be dominated by a smaller number
of competitive species.

I'm suggesting that in an aquarium that has been substantially unchanged
for several years there may be a tendency toward dominance of our common
BGA.  I don't suggest that as a reason for normal BGA outbreaks.

[snip -- here and there]
> But are our tanks like lakes and ponds or more like Streams?

They aren't very much like any of the above.  It is very difficult to
apply observations from natural systems to aquariums.  One very common
problem is that the organisms that cause common behaviors in natural
systems aren't found in aquariums.  For instance, we don't have many
daphnia or copepods in out tanks, we have a limited diversity among algae
and there is generally only one type of blue-green algae that is common in
aquariums.  As a result, most generalizations based on natural systems
will be wrong when applied to an aquarium.

I suggest with caution that the natural correlation between high stability
and a tendency toward dominance may carry through to aquariums.  I don't
feel real bad about doing that because the correlation is common to a wide
variety of natural settings; reefs, estuaries, reservoirs, forests,
deserts, prairies, alpine meadows, and on and on.  It is not dependent on
the behavior of any one organism or even any group of organisms.

Further, you can actually watch this happen among the plants in a planted
tank.  If you let a tank go for a while you end up with just one or two
plants taking over and squeezing everything else out.  If you want to
maintain a variety of different plants in a planted tank then you have to
get in and prune, remove extra plants and move plants around; that is, you
have to disturb the system. Since it happens to plants in a planted tank I
suspect it may also happen to other parts of the tank population as well.

> > At any rate, the last of my 15 year old Botias died last month, so I
> > decided to do something about the tank.  I removed all of the rocks and
> > tiles from the tank and bleached them and cleaned as much of the BGA out
> > of the tank as I could.  I removed some sickly plants while I cleaned and
> > thinned some overgrown patches.  After the cleaning I treated the tank
> > with erythromycin for three successive days, and doubled the dose on the
> > last day.  I left the filter media in place during the treatment so that
> > even the filter media was treated.  I increased the lighting at the same
> > time.
> A blackout and KNO3 would do better and cost less and be less work. Sorry
> about the fish though.

There are a number of different changes I could have made that might have
discouraged the BGA.  I could not guarantee the success of any one of
them.  Moreover, I wasn't interested in handing the BGA a setback. I
wanted to reset a long-term trend, and a heavy antibiotic treatment seemed
like a much easier choice than the next alternative, which was a complete
tear down and rebuild.

I think that antibiotic treatments are a terrible way to manage a tank,
and I don't ever recommend that anyone use antibiotics just to knock down
a bga outbreak.  There are better ways, and a blackout and KNO3 routine
might be one of those.
> > After the antibiotic treatment I rearranged some of the plants in the tank
> > and transferred some new plants in from other tanks.  I wasn't ready to
> > add CO2 to the tank, so I'm trying Seachem's Excel as a carbon suppliment.
> > I need to throw in some ramshorn snails to keep the leaves clean.
> I've certainly found a method around using antibiotics for BGA algae.

There are several methods, but I would be very surprised if any non-lethal
method (including blackout and fertilizer) is going to be 100% effective
for anyone, much less for everyone.  Different problems have different
causes and need different solutions.
> I think it's more likely poor conditions that favor the BGA's(high light/low
> nutrients/stagnant water) and not so much a resistant strain.

People on this list have reported severe BGA outbreaks under a wide range
of conditions -- many of which are "good" conditions by any measure.  One
thing I can say without any fear of being wrong is that the common green
slime BGA that we get in our tanks is *not* uniquely linked to high light
and low nutrients.  In fact, it is probably more common in polluted tanks
with low light.

Tom, could the idea that BGA is favored by high light and low nutrients be
one of those observations from natural systems that doesn't apply very
well to aquariums?  That might be possible because the BGA that create
that trend in natural systems are not common in aquariums or because in
the controlled environment of our tanks there are other more prominant

Roger Miller