I don't believe there are many long-term tanks out there that are 100% ich free 100% of the time. I'm sure there are some but you'd have to be so diligent. Quarantining corals, snails, crabs, macro, etc every time with out fail and never cross contaminating. Doable, sure....
Ich is easy to manage. Keep the fish well fed, their stress low and your water quality up and it's managed.
I had a decent outbreak a year and a half ago. I always bought quarantined fish. A wrasse got bit by something in the tank, ended up passing and boom, ich on half the fish in the tank.
Mixed Selcon in their food for a few weeks and it went away. I have tangs in the tank too. I haven't seen it since. I still buy quarantined fish.