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> I do wonder if keeping an aquarium under pretty much constant conditions
> for a long period will eventually lead to a BGA outbreak.  Natural
> environmental conditions almost never stay constant.  Perhaps in an
> unnaturally stable tank the BGA ultimately gains an upper hand over other
> bugs and takes over.

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
     Natural successions in lentic systems are well documented.
There is the spring turnover which generally has high nutrients and Si which
causes a big Diatom/small green bloom. These guys are growth specialist.

Zooplankton kick in and start eating and multiplying like mad. Si supplies
drop out of the water column from zooplankton eating/algae death and the Si
shells take a long time to dissolve back into solution thereby limiting
their growth after some time has passed.

Then you get a clearwater phase from massive herbivory(Daphnia, copepods
population explosion). There's still enough nutrients for algae growth but
the herbivores have eaten all the food.
    Gelatinous green algae comes in since it's not very tasty and many
herbivores won't eat it and then when the nutrients are further depleted BGA
makes a big appearance. These are more storage specialist. These are the
algae your not going to beat up using starvation methods.

Gelatinous greens are not as good as the smaller growth specialist but have
a gelatinous sheath as protection so they have their niche. But they have a
rough time later as the BGA's move in(during much of the highest light part
of the year).  By late summer, only motile algae and storage specialist can
get nutrients when they encounter nutrient patches. Autumn has a slight
increase in nutrients being suspended back(from fall water column turnover)
and some Si (finally being redissolved again) so you get some Diatom blooms
later in the year which do very well at lower light.

But are our tanks like lakes and ponds or more like Streams?

> 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.
> 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.
> So far it's working pretty well.  The BGA is gone and I hope that the
> treatment and the changes in the tank will reset whatever trend it was
> that let the BGA gain dominance.
> If you used erythromycin in your tank more than once recently and the
> BGA returns quicky then your tank may have developed an
> erythromycin-resistent strain.  You may need to use something else next
> time.  Last time I checked, copper still killed BGA.

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.

I used to have that dang band along the front of my tank's gravel. It
appeared where there was more ambient light hitting the tank. I noticed
though that with good nutrients and less light, it doesn't grow. These guys
like lean tanks with high light and little movement. Add movement, KNO3 etc,
blackout if you see them and they will not be a pest.
One tank that I saw not long ago has BGA only on the window side(the other
side was clean) and mainly only deeper in the gravel and the tank was lean
nutrient wise. CO2 seemed to have little effect perhaps even encouraging it
if the plants are left without nutrients against BGA. Blackout works very
well and KNO3 additions usually take care of the long term issues. This also
can be applied to many algae.

A number of companies sell products etc for algae but this has to be the
simplest long term solution for most algae. Doesn't cost a thing, hurt fish
or plants. Hard to make $ on this though..................

Tom Barr