Yes, it is possible to import ich by buying an invert, rock, or equipment from a tank in which the fish are infected. I did it once myself. I bought a couple of inverts out of a tank with fish. At the time the fish did not have any spots. A few days after I bought the inverts and put them in my tank the fish began to get white spots. I always quarantine my fish and hadnââ"šÂ¬Ã¢"žÂ¢t bought any new ones for years so I had to figure out where it came from. I went back to the LFS where I bought the corals a few days earlier and found his tank now had a full-blown infection in it. I donââ"šÂ¬Ã¢"žÂ¢t buy inverts out of tanks that contain fish any more, regardless of whether or not I can see spots on the fish.
Ich tomonts are not particular about what they attach to. It can be glass, rock, inverts, equipment, or most any hard surface. Then they can hatch after they have been moved. You donââ"šÂ¬Ã¢"žÂ¢t need to tear down your tank. You can get rid of the ich in the tank by taking ALL the fish out for 30 days. The ich will die without its food. Meanwhile treat the fish in another tank with hyposalinity. If you have a fish only tank without live rock you can use hypo right in the display.
Importing ich on infected fish is not the only way to get it into your tank, but it is how the vast majority of infections spread. It is unusual to get ich in the display IF you quarantine all fish for a minimum of three weeks. I recommend that people go a step farther and treat all new boney reef fish with hyposalinity during the quarantine period. Hyposalinity is beneficial for new acquisitions for more than just combating ich.
It is possible to import ich with live brine shrimp but not likely. You would need to have perfect timing because the free swimming stage of ich can only survive a few hours without a fish. You can get ich from collecting natural seawater, but if you store it for at least 24 hours before you use it the free swimming ich would be dead.
Terry B