Hm, looks like you have your tank well under control. All the levels look great and you acclimated him very well.
I agree with you. The LFS probably had ich in their tanks, and because the fish probably got a little nervous when he was moved, his immune system dropped and the ich saw the window of opportunity open and attached to the fish's body.
At this point, I would just keep an eye on the fish and make sure to use vitamins and garlic in his foods to build his immune system. Kick Ich should work for you, but if it does not, I like Stop Parasite even more. I have found it to be more effective at treating ich. So, use the Kick Ich, because I know that does work sometimes, but if it does not and you see the fish get progressively worse, switch to Stop Parasite. Both products are reef safe (safe with corals, rock, starfish, shrimp, snails, macro algae, etc.)