Ich

I just noticed this morning that one of my fish has ich and wanted to ask a couple of questions:



1.) is the Ich due to the environment it was in at the LFS? It looked fine when I brought it home, or can it develop it in your tank?



2.) how can you treat it?



My water is testing 0 for Amonia and nitrites and 20 nitrates. Corals and crabs/snails happy and healthy.