I've read several books on koi diseases, parasites, etc. All of them emphasize
the importance of sending scrapings/samples to a lab or having a microscope in
order to properly identify the culprit and determine the appropriate course of
treatment.

OK, time for a reality check: First, the only way I have ever been able to net
a koi in my pond is to nearly drain it. This stresses the fish so much that I
will not do it again. In fact, the last time I did this, for a full year
afterward they would run & hide when they saw anyone at the pond's edge. So I
will not be able to get a scraping or sample of any kind.

Second, I do not have a microscope or a lab nearby so I'm forced to guess what
the affliction is and what treatment to start.

I tend to start with Potassium Permanganate, treating the entire 220 gal pond.
If I don't see improvement, I try Formalin. If that doesn't work I try
Limnozyme. I know this is a wasteful "shotgun" approach but it has worked
somewhat. Last year I lost 2 koi to some kind of ulcer/fungus thing before I
was able to get it under control.

Here's my question: If you can only guess at what the ailment is, how would you
treat it? What meds in what order? Is PP the best place to start? My fish
have just been through a spawning episode and several are now showing whitish
bumps on their fins. One has skinned his nose pretty seriously. I started the
PP yesterday and have my fingers crossed. Any advice would be much
appreciated.

~ Gary
Zone 6b