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Re: Aquatic Plants Digest V4 #1126

       To: aquatic-plants at actwin_com
       Subject: Re: algae (adding N and P)
       From: Lazarus Miskowski <lazmiskowski at yahoo_com>
       Date: Mon, 2 Jul 2001 17:22:00 -0700 (PDT)

Arthur wrote:
With regard to adding N and P.  I don't do it.  For a
while, way back when, I added Potassium Nitrate.  I
was trying to dose to 5mg/L.  My test kit was aquarium
pharm.  I was finding that I had to add A LOT of
nitrates just to get the indicator to budge.  I even
tested my reagents on a saturated solution of KNO3
just to make sure they could budge.  And what did I
get for this effort?  Cyanobacteria.  My plants were
growing fine before I added N.  Then disaster after
adding N.  If it ain't broke, don't fix it.  I find
that the discus food provides sufficient N and P for
my plants.  I have yet to find the need to go down the
Lamotte-dose-your-own-N-and-P road, and am not sure if
it is necessary.  But then again, I've had 2 dark
hair-algae and 1 green hair-algae outbreak in the
tank's 1 year history.  Maybe the odds I am playing
aren't so great.

In a high-light, high-CO2 setting, plants pull down nutrients rapidly, and
when something gets deficient, then there is a window of opportunity for
algae to gain a foothold.  Before we try to compare Arthur's observations
with those of Tom Barr, we need to determine if Arthur has high-light, high
CO2 conditions.  As Tom said, if you add one nutrient, such as nitrate, the
plants may pull down another, such as PO4 more rapidly, then a deficiency
shows up, plant growth slows, and algae can get its little feet in the

One thing that I have seen on several occasions has been that adding N and
P can cause bluegreen algae to become more edible, and the snails, which
were previously not fluorishing, begin to eat, grow and lay eggs, and they
soon eat up all the bluegreen algae.  Apparently, if BGA grows under
conditions of nutrient paucity, it is a lot less edible or digestible or
nutritious.  Perhaps the snails eat some but do not get enough protein to
grow.  Or, perhaps there are toxic compounds which build up in
nutrient-deficient BGA, which are at much lower levels in well-fertilized
BGA.  BGA is a well-known porducer of a variety of toxins.

Paul Krombholz, in  central Mississippi where we have received above normal
rainfall for the month of June.