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bga and post-erythromycin cloudiness

Hello.  Here's a familiar situation with Bluegreen algae which has generated
several interesting questions.

I have a heavily planted 72 gal aquarium which is also heavily stocked with
fish.  Rapidly growing BGA appeared about two months ago (rather out of
nowhere) and has covered certain parts of the gravel and plants, leaving
other parts untouched (which is a peculiar, regularly commented upon
phenomenon with this pest).  It was very fast -growing, so that no amount of
"vacuuming" could keep up with it--it simply reappeared daily.  Water
quality in the tank was fine-low phosphates, nitrates, etc. (There is a lot
of material in the literature about this.  While bad water quality may lead
to BGA outbreaks, in my view there is no degree of good water quality which
will make it go away, and it's appearance may have nothing to do with water
quality at all--as in my tank, which is a case in point.  Nor can plants
outcompete it.  Nor is there any biologic cure for it which will not
jeopardize the whole plant tank.)

I finally decided to use Maracyn.  24 hrs after introducing 1000mg. into the
tank there was positively no regrowth of the stuff, and it was literally
"gone".  There is confusion over the proper dose.  I chose to treat the tank
with an additional 1000mg 24 hrs after the first dose to avoid a recurrence
(i.e. recurrence, not resistance, by the way).  24 hours after the second
dose the tank became cloudy, and there was still no bga in site.  I
concluded that there was a "cure" (i.e. a complete kill) of the bga, and
have now place Purigen back into the Fluval canister filter that I'm using,
and I made a 10% water change.  There has been no change in the last 48 hrs
in either ammonia, nitrate or nitrite.

Post-erytho cloudiness has been reported before in this situation at 14
days, but not this soon.  The question is what is going on?  Possibilities
include a kill of the filter bed although here I'd expect a change in water
quality (which may be coming?).  Can erytho kill the filter bed in a dose
related fashion (it usually kills gram positive bacteria only, while
nitrosomonas and nitrobacter are gram negative)?  Could  the cloudiness
relate to decay of dead BGA (the "effect" reminds me of what sonnicated
bacteria look like in my days in college biology)?  Could the cloudiness
somehow come from the erytho itself?  Would a lower dose or a single dose
have avoided the cloudiness?  Could a lower dose lead to a recrudescence?
Other possibilities?  Other suggestions?

In terms of "cure" another fact that I don't know is whether bga reproduces
by spores.  If so the erytho solution will be temporary because it will not
affect spores (nor does anything else for that matter).  Are spores part of
the reproductive apparatus of BGA?

I am not panicking.  The fish look fine.  But the questions and observations
are interesting, and maybe you can help.

(By the way there is one other peculiarity which I can't explain.  I have an
airstone in this tank. 6 hours after I introduced the first dose of Maracyn
the bubble diameter off each individual bubble shrunk significantly, and the
velocity of rise of the bubbles slowed.  Why?)

Thanks so much.

Robert A. Sirota
Huntingdon Valley, Pa.