I think this success is a direct result of not quarantining or medicating. I haven't dealt with any decease and I have never done either. My yellow tang did have HLLE but that was not a result of a pathogen. I believe that a fish has the immune system to fight anything in a tank, ich, velvet, whatever. When we expose them to the stress of a small quarantine tank that we are constantly medicating and messing with and then put them in the display, an environment completely different from the QT, that amount of stress seriously impacts the fish's immune system and makes them more vulnerable to disease. It is counter productive. Fish live their entire lives in a soup of pathogens, parasites and disease so they have evolved an immune system that allows them to do it.I am sorry and you can make up your own mind but I feel "all" fish can become "totally" immune from every communicable disease. There are a few tanks on here that are long running and never had any disease.
My own reef just hit it's 50th birthday and no fish in about 40 years has had any communicable disease. I have not lost one fish to disease in that time and I have never quarantined or medicated.
It is very easy but many people on here will just tell you it is luck so I am going to keep my tank running another 50 years just for kicks and at 100 years old I will see if people still think it's luck.
The Other Way to Run a Reef Tank (no Quarantine)
The other way to run a reef tank (No Quarantine) I was asked by my friend Humblefish to start a thread on my practices of running a tank with no quarantine, hospital tanks, medications, dipping or almost anything else. It is "not" just to take a fish from a store and drop it in your reef...www.reef2reef.com