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re: need help identifying deficiency
Over the weekend, Jon Wilson asked what deficiency might cause his anubias
to develop little whitish yellow spots that eventually turn into holes.
Briefly, I think the symptoms might show a deficiency of either magnesium
or potassium, but that adding more of either magnesium or potassium may
not be the right solution.
The a. barteri nana in one of my tanks did this a couple years ago. I
initially attributed it to over-vigorous cleaning by a breeding pair of
Mesonata festivum. I sold the pair and the symptoms didn't disappear. In
fact they got worse and the problem turned out to be the first of a
complex of symptoms that have plagued that tank ever since.
The complex of symptoms included deformed new growth, early leaf loss,
light colored leaves (not normal chlorosis), lesions and necrotic areas on
the leaves. Different plants showed different symptoms. Some of the
symptoms affected leaves exposed to direct light while shaded leaves
showed no symptoms.
I think the whole complex of symptoms indicated a shortage of calcium,
magnesium and potassium. In your case I think the spots on the leaves
could indicate a deficiency in potassium and/or magnesium.
Your test results show what should be a sufficient magnesium content.
Also, I seem to remember that the Dupla fertilizers carry quite a bit of
potassium. It doesn't seem like a shortage of either potassium or
magnesium is very likely.
In my case the deficiency symptoms seem to be caused by the combination of
excess of sodium in the water and high (3 watts/gallon) light levels. The
sodium seems to interfere with the plant's uptake of calcium, magnesium
and potassium, and the high light level guarantees that whatever nutrient
is least available limits plant growth. Growth limited by calcium,
magnesium or potassium comes along with deficiency symptoms.
In your case, I'd try to find out how much sodium there is in your water.
As a practical matter, you can't really test for sodium yourself, but you
can get an analysis from your water supplier. If you use artificially
softened water the sodium will probably be high. Your water supplier
probably won't be able to help you with that but maybe the water softener
reseller can. If you use sodium-containing additives (baking soda, for
instance) that can also boost sodium to detrimental levels.
If your sodium is high, then I'm not sure what you might do about it; what
you do depends on why it's high. Reducing the lighting might also help.