I QT everything, corals, rock, algae and inverts usually get 2 weeks, fish get 8-10.
My tank has ich, always has, (even thought I don't see it), I don't make it a secret. I originally thought it was from a fish that I did not QT because I knew where it came from, etc (stupid, I know), but after a lot of thought, I really think it came from inverts that I did not QT. They were in a tank with fish at the LFS, and the fish had ich. Live and learn. Now I have ich and I deal with it.