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Re: bluegreen algae control

Roger S. Miller believes that he reduced the blue-green algae in his
tank by providing conditions that encouraged green algae growth.

>I've struggled with bluegreen algae (cyanobacteria, cb)  outbreaks on and
>off for years now, and I've made a few observations that I'd like to throw
>into the mix. In short, I think cyanobacteria and green algae compete in
>aquaria.  Cyanobacteria bloom when they get the competitive edge and the
>blooms can be controlled and reversed by swinging the competition back to
>green algae.

We've all struggled.

>Most of the times I've seen cb problems develop, the cyanobacteria
>progress from barely noticeable to tank - dominating over a period of a
>couple days to a couple weeks.  Once the cb are established, no amount of
>cleaning, water changing or most tank management changes can get rid of
>it.  Once it's there, it's in control.


>Cyanobacteria outbreaks have ended mostly with chemical treatments.  I've
>found that copper sulfate, erythromycin and other antibiotics can wipe out
>cb populations.  On one or two other occasions, the outbreaks ended
>without major effort.  In those cases, the demise of the cb was
>accompanied by accelerated growth of green algae.

If it was truly competition, then green algae should have prospered
immediately after the destruction of the cyanobacteria by the erythro-
mycin, and not just on those occasions when the "outbreaks ended
without any effort." I believe the green algae caused the shrinking
of the blue-green algae, but not through competition.

>I decided that the pattern of cb occurence - blooming from negligible to
>dominant without obvious cause, a tendency to stay dominant once
>established and sudden disappearances coupled with an increase in green
>algae growth - indicated a competitive relationship with green algae.

Those bacteria divide quickly don't they.

It just means that each type has a preferred environment, and may try
to maintain those conditions which favour its growth.

>I tested this idea.  I had a tank with cyanobacteria and no evident green
>algae.  The tank had no fish and a moderate population of low-light plants
>that mostly seemed uneffected by the cb.  I decided that I would generate
>conditions I thought would favor green algae and see what that did to the

Conditions that favour green algae also tend to favour macrophytes.
You also have plants in your tank which benefitted from the better
lighting and increased nutrients.

>I increased the lighting from 1 watt/gallon to 2.5 watts/gallon, removed
>the media from the biological filter, started adding a major nutrient
>fertilizer with ammonia and continued weekly cleaning and 15% water

Although your statement mentions no quantities, it would seem that
there was more than enough light and nutrients to provide for both
types of algae. So how do you explain the disappearance of the

>The response was nearly immediate, but not spectacular.  The tank
>developed cloudy water (phytoplankton) and judging from the amount I
>removed at the next cleaning, the cb growth rate dropped to about 1/2 it
>previous level.  The cb growth continued to decrease for about a month.
>At one month I noticed green algae growth on the tank sides and after the
>next tank cleaning, the cb was rare.  Now its two weeks later and the
>cyanobacteria aren't visible.

As the mass of green algae increases, so do oxygen levels in the
tank. This starts to inhibit the reproduction of the cyanobacteria,
The older bacteria eventually die out except in those locations least
aerobic. There they await the return of more favorable circumstances.

>This sounds a lot like the results that DWebb reported a couple months ago
>from ammonium sulfate addition, but without the severe buffer depletion
>that he reported.
>I don't have any reason to believe that higher plants compete with cb the
same way that green algae seems to.  That is, I've never seen that adding
\>more plants to a tank helps control cyanobacteria.

I do. I can manipulate the advance and retreat of cyanobacteria by
worsening or improving the conditions for the plants. One is not only
controlling nutrient uptake, but also oxygen levels in the tank.
The blue-greens appear to me to have a limited ability to tolerate
oxygen in the water.

Floating plants, even when growing quickly and sucking up nutrients,
don't seem to have the same effect upon the blue-green algae. Often
one can see the cyanobacteria attached to the undersides of water
lettuce, water sprite, or lotus leaves. I attribute this to the fact
that the plants are pumping oxygen into the atmosphere and not into
the water.

If the plants are producing lots of oxygen, a circulation pump works
wonders in evenly dispersing that element throughout the aquarium.

That's my theory. Horeman and Rataj, and at least one other author
casually mention that cyanobacteria and oxygen don't mix well, but
don't go into details.

Dave Whittaker
ac554 at FreeNet_Carleton.ca