Where to begin? O.K., I have several Dendrobiums (most from section
Dendrobium) that are showing similar symptoms.

1. The thin leafed types begin yellowing at the tips of the middle to
older leafs. Eventually they start turning tan in color, dying back
from the tips.
2. Those with a thicker leaf consistancy also begin yellowing at the
tips or somewhere along the margin, but are much slower in actually
dying and turning tan in color. Some do not begin dying off. They
simply become chlorotic in spots.

I have treated for both bacterial and fungal infections to no avail. I
am beginning to suspect mico-nutrient deficiency or toxicity.

Up here, we have water quality most of you would die for, very low in
disolved minerals and other such things. Visiting guest speakers for
the local O.S. have often recomended that we feed with every watering
because out water is so clean and free of contaminants.

I use a fertilizer mixture of:
A crystaline 10-52-10 with a label assay of:
N:
9.0% Ammoniacal
1.0% Nitrate
P:
P2O5 52%
K:
K2O 10%
Boron: 0.02%
Copper: 0.07%
Iron: (Chelated) 0.15%
Manganese: (Chelated) 0.05%

The other fertilizer ingredient is a 0-10-10 fish based fertilizer
with a lable assay that includes:
Chlorine: 8.0% (That strikes me as high.)
I chose this material because I assume the marine fish base should
supply any and all micro-nutrients that might be needed.

I fill a tub with 6 gallons of water and add the recommended amount of
each fertilizer for 1 gallon. To my thinking this is the equivelant of
adding a 10-62-20 requirement for 1 gal to 3 gallons of water, a 1/3rd
solution. I fertilize at almost all waterings during spring, summer
and fall, and few if any during winter.

Potential causes as near as I can deduce a
DEFICIENCIES OF:
Magnesium
Cobalt
Copper
Iron
Manganese
Molybdenum
Nitrogen
Zinc

EXCESSES OF:
Calcium
Chlorine(?)
Potassium
Phosphorus
Zinc

Can anyone comment or add any insight to this possible problem?
Thx
S V