As I read this post, I say kudos to dangles as he figured out in 2 years what took me 50 years.Did they add the rock to an existing tank? If so, did they have a "clean" test prior to that? If a new tank, did they transfer fish/corals into the tank along with the live rock? Maybe not, but all are relevant questions worth asking.
I think it's becoming more and more clear that ich (and many of the other "big nasties") exist in tanks that don't exhibit any symptoms. Many more tanks than most people realize most likely. I'd be curious if 100 random people tested their tanks, how many would pop positive on one or more parasites/diseases without symptoms.
To the OP... I've only been in the hobby for a little over 2 years so my experience is obviously limited. Take my opinions as just that... opinions. But in that short time I've already evolved from "QT ALL THE THINGS!!!" to "buy from trusted sources, try to keep everybody healthy, well-fed and minimize stress.... and try not to stress yourself too much." Take reasonable precautions for sure. I will only buy pre-QTd fish from now on because I DO have a verified clean tank. But beyond that, I don't stress too much about it. I won't hesitate to add live rock/sand in the future. But I get it too. It's easy to get overwhelmed with info and anecdotal opinions on the forums![]()
If healthy fish in the wild are host of dormant ich, indicating that the fish immune system holds pathogen in check and/or environmental conditions are holding dormant cyst in check, it seems logical then that maricultured fish in sanitized mariculture facilities have fragile immunity to pathogen invasion.