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Re: Green Water / BGA

> Date: Sat, 25 Nov 1995 19:07:36 -0800
> From: Pat Bowerman <bowerman at specent_com>
> Subject: Green Water
> Steve Dixon wrote:
> > > Since I'm on a roll, how about a 3rd question?  I've been practicing
> > > "patience" with a green water problem in my 3 mo. old rainbow tank.
> > > I've been testing to see if anything unusual is going on.  The biggest
> > > surprise is nitrates.  Despite the fish load and the addition of 4-8
> > > mg./l nitrate (from KNO3) at water changes, the nitrates drop to 0.0
> > > (LaMotte) within a few days.   Other tank parameters:
> > >
> > > 40 gal. reg; pH 7.2 (mornings) ~7.4 (afternoons); GH 5; dKH 10
> > > CO2 12-20 mg./l; phosphates - always 0.0 (Hach)
> > [BIG SNIP]
> Mark Pearlscott wrote:
> > This is very interesting.  Both your nitrates and phosphates read zero?
> > What is your turbidity like?  How often do you test the tank water?  How
> > often do you do the water changes?
> > 
> > It's true that most micron cartriges have a hard time filtering out
> > green water.  You might try one of those particulate binding
> > (coagulating) products to see if that does the job.
> I had a similar situation. NO3 and PO4 measured 0 despite daily
> additions of PMDD. Iron also measured near 0. Still the green water
> flourished. This would seem to indicate that the green water is very
> efficient at removing nutrients from the water. During this time, I had
> no other green algaes present in the aquarium. The only other algae
> present was some dark brown to black filmy stuff that was hard to
> remove. An H.O.T. Magnum with the micron cartridge in had no effect on
> the algae.  
> Roger Miller wrote:
> <Snip>
> >    Green water blooms were related to iron fertilization.  I stopped using
> > it and the green water disappeared quickly.  I let the tank stabilize and
> > afterwords I was able to gradually worked the fertilizer back up to a
> > useful level.
> This makes sense. Roger, how did you "let the tank stabilize" ?
> Pat Bowerman

Okay... I must bite at this one (again).

I wasn't thinking too straight when I replied to Steves post originally,
but let me straighten things out now.  I first need to agree with
Roger.  Green water is related to iron, but only as all plants need iron
for growth.  Right there is where I must differ in opinion.

Green water seems to grow, but only when the conditions favor it over
other plants.  In aquariums where nitrate is the limiting nutrient, and
phosphate is in excess, green water (unicellular algae) does great. 
Both can be un-measurable by test kits, and here is why:  With nitrate
being limiting, this asserts that everything else is present in larger
quantities.  Phosphates only need to be in slightly higher quantities. 
They can still be below test-kit range be being used up as soon as
nitrate becomes present, even in the most minute amount.  In addition to
a constant presence (however low) of phosphates, the depletion of
Nitrates puts the higher plants at a disadvantage.  Higher plants are
better at competing when nutrient levels are more "balanced".

So now knowing that having nitrate being a limiting nutrient supports
green water growth, it is easy to eliminate it without filters,
additives, medications, etc.  Just add nitrates to the tank (KNO3 works
well).  By SUSTAINING a low level of nitrates (3-5ppm) in the tank, you
force the nutrient balance to shift.  This will cause phosphates to
become limiting.  Given time, this will cause the plants to thrive and
green water to fail.  Be patient, as it does normally take a little
bit.  A lot does depend on how turbid the green water is, how many
plants you have in the tank, how much you fertilize (and what you
fertilize with), and the bioload of the tank.

This would also explain why some tanks just seem to "automatically fix
themselves."  Here I would suggest that the biomass has contributed to
rising levels of nitrates, causing the balance shift I talked about.


Okay, slightly off the green water (though still there really)... Has
anyone with a green water outbreak had BGA left afterwards?  I have a
theory that in addition to unhospitibal nutrient levels for BGA, in
addition to reduced light, green water could be helpful in destroying
BGA.  If it is true (and at this point I am just guessing), one could
force a green water bloom to kill off BGA, and then re-adjust the
nutrients to clear the tank.  I would be very interested if anyone has
had BGA that survived a green water bloom.  Any comments are welcome.


pearlsco at u_washington.edu
Complication, Depression and Stress have the power to put one on the
right track of life.