I am a bad bad gardener.

My phals look like the teenage kid working at the local greasy spoon
restaurant. They have plant acne.

Actually, I noticed that the phals (and the dendrochilum) had been hit
with something that caused pitted spots on the tops of the leaves. Some
of the plants have interesting designs where the leaves were infected.
I believe it to be contact related because a few leaves that were turned
upside down had the problem on the bottom surface of the leaf.

The Cattleyas, Oncids, Cymbos, and other stuff seem to be unaffected.
This crud really likes those nice succulent Phal leaves.

My suspected sources a

The swamp cooler that I did not change the pads like I should and
something bloomed on those nice moist aspen wood pads then got sucked
into the greenhouse. I promise to keep a closer eye on the swamp cooler
from now one. I promise (unless of course I get busy with something
else and put it off until another day like I normally do).

Another possibility is that when I cleaned the greenhouse with the
pressure washer something that normally would be on the concrete floor
got into the air and settled on the leaves. The floor of a greenhouse
is one of the dirtiest places on earth.

The third suspect was the bucket I use to mix fertilizer for the
Dosamatic. I may (ok I used to take shortcuts) not have cleaned it up
very well before I used it between waterings and something was growing
in the cesspool of old fertilizer.

So, here is my question. I want to start a regular spraying of Physan,
specially on the phals. I see where Ray recommends 1 tsp to a gallon
for plant contact.

How often can I apply Physan to the plant leaves at this rate?

What would I see if I am applying it too often? (Leaves burning, flowers
deformed, etc.)

Any other ideas of what I should do to prevent this crud from returning?

I am fanatical about cleaning up the dropped flowers and dead leaves in
my greenhouse. I keep the humidity very high in the winter and as a
result I get algae and moss growing under the benches and on the glass.
I clean it up periodically but it does return.

Thanks,
Gene