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Nitrogen deficiency ?

I have an Hygrophila corymbosa with yellowed leaf tissue growing in my
49 gallon tank which has recently had a new substrate installed. The
substrate is layered: 1 inch of subsoil, sand and 1 pound of Micronized
iron; 1 inch mixture of peat and sand with 60 grams of FTE (fritted
trace elements) covered by a layer of regular aquarium gravel. If I
repeated this, I would mix a low organic garden soil with the sand and
peat. The substrate is producing bubbles of what are probably nitrogen
and is 5 weeks old. There are regular additions of chelated Fe & trace
nutrients weekly (twice weekly for the last two weeks) of 1 ml of
Flourish. I've been changing 25% of the water each week and dosing with
10 ppm of K+ and Mg++ (sulphates) and 1 tsp of CaCO3. The tap water in
Vancouver is extremely low in minerals. Lighting is a 250 watt metal
halide pendant with the bottom of the bulb 14 inches above the water
surface. The tank is 1'x4'x18"ht. CO2 is fertilized at 1 bubble / 4
seconds into a powerhead with an 8" hose attached to the outlet.

There are about 40 fish with an average size of 1.5" which are fed
moderately. I have not added (until now) any source of chemical nitrates
aside from fish food and the peat in the substrate. Just before adding
the Flourish I cannot measure any Fe using the Red Sea Fe test kit. I
also cannot measure any nitrate with the Tetra test kit.

I have no other plants showing overt deficiency symptoms except slow
growth. Many of the Crypts had their old leaves melt in the first week;
most of them had been grown in a nitrogen rich environment previously.
The nerves of the leaves are green and are surrounded by a light green
area which fades to yellow at the leaf edges. At this time both old and
new leaves are all affected similarly. I have removed several of the old
leaves which had begun to deteriorate. At this point, I was pretty sure
that I had either iron or nitrogen deficiency. I suspected iron
deficiency since it seemed to affect new leaves. With the increased
dosing of iron (twice weekly), small amounts of soft green algae have
formed on the aquarium glass. I interprete this as indicating that there
is sufficient iron even though the test kit indicates none a few days
after the dosing.

Last night I added about 1/3 tsp of KNO3 to the tank and will begin
dosing at the next water change with nitrate in addition to K, Mg & Ca.
I also added 10 clay balls to the substrate which have been prepared
with slow release 14-14-14 Osmocote and FTE near the roots of the
largest plants. I don't know if the Osmocote will release significant
amounts of K through the clay. I might reduce my overall K input if you
feel that the diffusion of K through the clay could be a problem.

After about 24 hours, the green borders around the young leaves appears
to be larger. Another few days should confirm that the symptoms were N
deficiency. Another tank with a slightly richer substrate measures about
5-10 ppm of nitrate and has an identical nutrient input. The fish
population in this tank is very light; perhaps 10 small fish averaging
1" in length. The same H corymbosa plant in this tank has light green
leaves with only a hint of yellowish-green. Growth of the Hygro in this
tank is also slow. In the past, the Hygro in this tank had displayed
similar yellowish tissue symptoms which I had interpreted as iron
deficiency. The Cryptocoryne balansae in this tank is also showing an
increased tendency to melt its older leaves which seems to suggest a
shortage of nitrogen. For me, Crypts grown in high nitrate conditions
have never showed any tendency to Cryptocoryne melt. What is throwing me
off, I think, was that the young leaves of the Hygro are showing the

Can anyone confirm my analysis?


A peat + mineral soil substrate may produce sufficient N under low to
moderate light conditions but may require supplementation under high
light conditions where other nutrients are not limiting. 

Sphagnum peat moss is fairly stable under submerged conditions and does
not release high amounts of nitrogen or phosphates. (as shown by

Hypothesis for testing:

Addition of about 1/2 pound of earthworm castings (1% by weight) in the
fertile mid layer together with 1 part peat, 2 part loamy mineral soil
supplemented with 1 pound of micronized iron would be a good substrate
to try. I'd also put a 1-5 inch layer of subsoil (hopefully iron rich)
in the bottom layer. If unsure of the iron content, add 1 or more pounds
of micronized iron. This should produce a moderately fertile substrate,
rich in trace nutrients and anaerobic bacteria. It should be rich enough
to support Crypts yet not too rich for a good variety of other plants in
a well lit aquarium with CO2 and adequate dissolved minerals in the
water as I described.

Steve in Vancouver where the heavy rains have subsided and sunshine has
returned (just in time for the work week!)