You can't. The good news is they are like a mass of jell-o if healthy: their slime coat is so thick that, if healthy, they almost never get ich unless the tank is an ich farm. This is one fish that (a) I am very careful where I buy and (b) you just take your chances and determine if you're willing to run the risk. Some people who have special reason to fear ich jury-rig a mandy feeder device, but keeping a rock-hopping obligate pod eater in a glass box for 72 days with a feeder going is not easy on the owner, though as long as there are pods, the mandy will probably be oblivious to all else. I confess I fall in the 'take your chances and buy a healthy fish' column, and have never had ich come into the tank with one. They'll live for many years if you do it right. Is the risk worth it? You have to answer that for yourself.