I "seem" to be pest free for almost a year now. I killed all the liverock I obtained by bleach followed by muriatic acid in a 150g trough. I then cooked all the rock after it was "clean" and jumpstarted it with an aquacultured (pest free) liverock and some organics to break down. I cooked/cycled the rock for almost 8 weeks while setting up the tank. I started both my displays (hooked together) with new sand as well.
That said...the only way to keep it fairly "sterile" of pests is a "true QT" system like TOG mentioned above. I think he meant you have to QT EVERYTHING. That means anything and everything that you put in your tank, to be 100% certain. Honestly, I found that to be basically unrealistic and impossible. I mean, I'm not going to QT clean up crew additions, etc. I have a small frag tank in my basement that all corals I obtain go into for at minimum a couple weeks. Mostly to see if any aiptasia or other pests turn up. It saved me some aiptasia problems a couple times. Otherwise, whenever you get frags from people/vendors you have no idea what their history is or what they might be carrying that is not obvious at first. Hence the QT process.
Obviously QT of fish is VERY important. It's much easier (IMO) to treat for aiptasia and other pests than it is to treat a reef for something like Ich. I can tell you, my time with QT'ing ALL my fish was not for the impatient. It almost pushed me out of the hobby before I really got started.
However, it's necessary if you want long term success (as preached by MANY experienced/successful hobbiests). I had marine velvet early on with a couple of my first fish, and it sucked. Starting the clock again anytime you get new fish is a true pain in the rear but definitely worth it in the long run.
I have never seen or heard on any forum and any researching of the topic, any hard evidence to support that Ich is ALWAYS present. As it is a parasite that needs a specific host [fish], if there are no hosts available it dies off (in theory). I can see the argument both ways, but again have never seen a solid fact-based answer to the question...either way. It is HIGHLY debated on national forums from my experience.
The more you put in your tank without QT observation the more chance you have at picking something up. I always dip my corals, QT and dip again before putting in the display. I always follow guidelines for fish QT as well. However, I've rolled the dice with good luck so far (fingers crossed) on putting in hermits, crabs, snails, etc in my tank without proper QT. I've seen aiptasia attached directly to the shells of hermits/snails before even at some of our favorite LFS's. Always a gamble without QT'ing everything.
