Willie, i wonder if you share the same attitude about introducing new "healthy looking" discus or any other healthy fish with your current stock ?
Do you QT new arrivals if they are healthy looking ?
I'm on the other side of the boat here being very paranoid about cross contamination , that's why I ask about your experience .
No, I'm fanatical about quarantine. New fish get their own tank for a minimum of six weeks. I typically buy batches of discus - almost never individual fish. They essentially grow out in their own tank until they pair off. At least one quarantine tank is critical to successful discus keeping.
Sponges, etc., are a different matter. One should know if there's disease in your own tank. If the discus are healthy, they stay in the upper third of the tank and face you during feeding. I'd have no hesitation moving sponges around thee tanks. I also have guppy and pleco tanks with a lot of sponges and move these into discus tanks with impunity.
Willie
At my age, everything is irritating.