MK - so glad to hear about the Blue Diamond doing better! I wonder if the "order within the pack" was simply being challenged with the reintroduction of the Blue Diamond to the main tank. How is it going now?

To provide an update to the Forum on my situation, the Quick Cure successfully eliminated the grey/whitish patches (which I think may have been Costia, an external parasite), but I am still dealing with a single fish who won't eat (hasn't eaten now for about 2 months). I suspect internal parasites is the issue with the non-eater, so I now have moved him to a quarantine tank and am beginning a heat treatment (slowly raising the temp of the water to 96 degrees over 3 days, maintaining it at 96 for 5 days, and then slowly decreasing it back down to 85). I hope this eliminates his remaining issue, and that after this treatment he begins to eat again.

Interestingly enough, while I am just in the 3rd day (just now getting the temp up near 96) of the heat treatment, the ailing fish has virtually stopped pooping. He was previously dropping 1/2 to 1 inch long white poop (despite not eating anything), but since being in the higher temps, he has essentially not dropped anything. I hope this is a good sign that indicates the treatment is beginning to have some positive effect?