Where does ich come from?

[schmidthouse]

How do you get ich, besides introducing a new fish into your tank? If you already have an estabished tank, can it show up out of nowhere?

 

[saltn00b]

part of the life cycle of ich burrows in a calcerous substance, so while it is very unlikely, it is not unheard of to introduce ick into a tank from LR, LS and even coral skeletons.