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Re: Nutrient deficiency? in hygro

> From: Pete and Kellie Schmidt <petes at nas_com>
> Subject: Nutrient deficienty/toxisity in Hygro. Polysp.
> I can't seem to figgure this one out on my own.  I have had hygro.
> polysperma that grew several inches a day in the past.  Over the last 6
> months, the growth has slowed, and for the most part, stopped.   The leaves
> have turned  reddish, but somewhat translucent, and seem to drop off easily.
> The goofy thing is that in several new tanks I have set up lately, I am
> seeing the same symptoms.  Substrates are soil-vermiculite gravel.  I dose
> with PMDD, supplementing extra KNO3, K2SO4 and Epsom salts to keep nitrates
> approx 5ppm.   I have never seen iron deficiency symptoms, so don't really
> know what to look for. The last water quality report I got (about a year
> ago) claimed 20ppm iron, and I have had hair algae problems in the past as
> well, so was never too concerned with iron deficiency.  Also, since my PMDD
> uses Plant Products Ltd trace element (7% iron, EDTA), I still think iron
> deficiency unlikely (I wish I had $50 for a test kit).  
> My question is:  Could the similar symptoms be caused by an excess of
> nutrients? 

	In the 160 L tank described in the original "Control of Algae
in Planted Aquaria" article that Kevin and I wrote, substantially
the same thing happened.  Several varieties of plant have given up
and others have taken over.  Hygro difformis and hygro polysperma
are two that have lost out.  The alternative explanations that occur
to me are either that some of the plants that are growing _really_
quickly are depleting the tank of some nutrient, or that something
is building up in concentration to the point where it adversely affects
some plants.  I have been adding phosphate to the tank lately, to
see what effect that has.  No significant algae have appeared, but
the Java moss and riccia fluitans seem to find conditions very much
to their liking.  Crypts seem to try to take over in every tank I'm
running, and Java moss gets everywhere as well.
	Another observation along the same lines is that in 160 L
"PMDD" tank, Frogbit and giant duckweed have given up, while
the riccia has to be thrown away by the handful.  In a 35 L, no-plant
nutrient addition, guppy tank (harder water, no CO2, higher pH)
the giant duckweed has almost taken up the entire surface, and the 
rest is taken up by Frogbit.  The riccia in there has gone.

	I'm afraid that I don't have any answers to the original
question, but have no doubt that nutrient deficiencies/excesses
affect the abilities of different plants to grow.  If you add 
competition for light to the situation as well, it gets very
complicated indeed.  What I would really like to do is to try
a few tanks with small numbers of plant species in each, and
see how they fare with different nutrient regimes.  I'm more than
a little too busy as it is, though.

Paul Sears        Ottawa, Canada