Another update for personal reference or for anyone else who may find this later...
I continued with the medicated feed. It should run out today. That's 4 weeks straight. No more dead fish. I am still seeing fish that don't look normal, but it may be scars instead of sores.
I held my breath during the past full moon since it appeared that the timing of the May spawn seems to have coincided with the majority of my fish deaths. I did sample the bedding areas with a fly rod one evening. I would catch one fish and move on. The sampled fish were much smaller than most of the ones caught prior to the fish kill, but were still in the 8-9" range.
As bleak as things seemed a month ago, the pond seems to still be doing well.
I sent off a water sample about 6/1 and am still waiting on the results.
