Originally Posted by Lumpy
That sucks. I've been fortunate and never had to deal w/ Popeye. I've had to deal w/ Ich, Columnaris, Swim Bladder Disease, Bent Spine, and Neon Tetra Disease though and what a pain in the ass! My water quality is pristine too, so I agree that there could be other factors that play into why fish get diseases.
Popeye is EXTREMELY easy to treat. The best thing you can do is aid medication absorbtion and protect the underlying tissue by swabbing it with Methylene Blue.
The biggest factor that plays into fish susceptibility to disease, IMO, is their origin. Neon tetras have a high mortality rate because they're genetically "watered-down". Some fish, like otocinclus catfish, are fragile because their wild-caught and the methods used are often very traumatic for the fish.
EDIT: I've had virtually ZERO opportunistic infections (Columnaris, Saprolegnia fungus, etc.) since installing a quality UV sterilizer.
FYI, male bettas make GREAT tankmates for community fish. You just can't keep them with fish that are notorious fin-nippers because they'll get abused and you, obviously, can't keep them with other male bettas.