I'm sure that some will disagree with my perspective, but I only worry about discus and angelfish disease. I don't see disease transmission from Corydoras, tetras, Plecostamus, dwarf cichlids to discus. (Just like I stay away from sick people, but not sick dogs, cats, etc.) I keep seeded sponge filters in my livebearer and Plecostamus tanks. When I need a new filter for discus, I just pull sponge from these tanks for immediate cycling.