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Re: Nitrogen Deficiency

Jonathan Kirschner <Jonathan_Kirschner at Energetics_com> wrote:
> It wouldn't surprise me if it is a deficiency of N, Steve, since H.
> corymbosa is such a fast grower.  It does however sound like you
> have an adequate fish population in this aquarium, as well as a fairly
> rich substrate.  Is the Hygro growing emersed? 

This Hygro is submersed but it is within a few inches of the water
surface. I'll probably prune the senescent leaves and encourage some of
the many side shoots to grow out. It has already been topped so it
probably won't get out of the water for a month or so. 

I had anticipated more nitrogen availability in this tank from the peat
and the fish food. There was no other source of nitrogen in the
substrate aside from peat. I wanted to evaluate how much nutrients the
peat would supply. The nutrients appear to be sufficient to sustain
moderate or low growth rates. When I used a substrate containing more
labile organic materials (earthworm castings), I found that the
substrate released nitrogen and phosphorus in large amounts for a long
period of time despite frequent water changes. Nitrates are extremely
soluble and when released by decomposition, they find their way into the
water column very rapidly. I think we can assume that there will be a
higher concentration in the interstitial water of the substrate and
occupying cation exchange sites.

When we talk about substrate materials, it is good to qualify which
aspect of richness. This substrate has only peat as an organic material.
There is subsoil however, this has almost no organic content. Iron and
other micronutrients from fritted trace elements and micronized iron are
present and I have limited the FTE to 30 grams which is about two or
three tablespoons. FTE is 7.5% Mn, 18% Fe, 7% Zn, 3% Cu and 0.2% Mo in a
soft glass frit (glass mixed with minerals and fused into a porous
glass). I don't know how rapidly these nutrients are released but I
suspect that with the glass material it will not be rapid.

> I would not advocate
> throwing nitrates into your tank unless you are sure you need them,
> but in this case the addition of the KNO3 really seems to have
> helped.

Yes, certainly the available nitrates were being used up very rapidly.
The relatively slow growing plants like the Crypts, Bacopa etc. were
finding enough nitrates from the substrate to avoid overt symptoms. The
dose I used was calculated to bring the NO3- concentration to 10ppm and
a test last night has confirmed that. The most obvious change has been a
growth spurt from H polysperma variegated (incidentally no yellowing on
this plant) The young leaves of the H corymbosa have definitely greened
up. There is not much change in the old leaves. The middle leaves showed
some increase in green however the edges are still yellow and there is
no further greening. I think those edge tissues are dead now so may not

I have a feeling the H cory is a big plant used to having a large root
system from which to draw nutrients. When you transplant a big fellow
like this into a new tank and it doesn't have a lot of roots, it's going
to be at a disadvantage for a while. This one had only "waterborne"
roots and was a large cutting from the top. Maybe I'm premature in
saying that the peat isn't giving enough nutrients. There are advantages
to controlling growth rates too.

Steve Pushak in windy, rainy Vancouver.