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Magnesium deficiency
Alex Holeczy wrote:
> I have been reading up on aquatic plant nutrient deficiencies to see if I
> can determine why the plants in my tank are not growing well.
> The description for magnesium deficiency seems to fit. The leaves on my
> giant hygrophila are pale green to yellow colored with dark green veins
> and they is barely surviving. My crypts also have dark lines on the
> leaves, as if someone marked them up with a dark felt tip pen.
[snip]
Are there other things which cause the plants to grow this way?
The symptom you describe on the hydrophila is interveinal chlorosis. It
can be caused by several nutrient deficiencies, including shortages of
iron or manganese. Chlorosis (usually of a more general nature) can also
be caused by shortages of nitrogen, sulfur and molybdenum to name a few.
I don't really know what symptom you are describing on the crypts.
When you use symptoms to diagnose deficiencies you should pay special
attention to whether the problem is seen first in old leaves or in new
leaves, at the margins of leaves or in the middle. These details may help
narrow down the possibilities. Magnesium deficiency, for instance should
appear first in the older leaves, while a manganese deficiency appears
first in new growth.
If you believe your tests, then your water should have sufficient
nitrogen, iron and magnesium (as a normal part of the hardness). It is
possible -- but fairly unlikely -- for your general hardness to include so
little magnesium that you could have a deficiency. According to at
least one source it's also possible to overdose with potassium and cause
a magnesium deficiency as a result of the imbalance between potassium and
magnesium.
You can safely dose with MgSO4 to see if you do have a magnesium shortage.
This test might not be diagnostic if the problem is caused by excess
potassium.
Roger Miller