It’s a much about getting a well conditioned specimen as anything else. Achilles are naturally programmed to be grazers eating food over a long period of time. Many don’t acclimate to aquarium life because they’re initially shy eaters, easily bullied, and aren’t inclined to eat one or two meals a day during feeding time. This is why it’s important to get a specimen from a shop where it’s isolated and offered nori or cracked clams around the clock.
While I’m not anti-quarantine keeping an Achilles in anything less than a 55 gal is going to be detrimental to the fish’s health. They need live rock to pick on and good palaces to hide. Most QT setups I see are smaller bare bottom affairs. So, you’ve got to weight the good and the bad.
Now, you’re never going to rid your tank of ich. That’s a fact. However, having a stable mature aquarium and a good plan to combat out breaks is the next best thing. I introduced my Achilles directly into my DT after he was conditioned at my LFS for a week. Tank is a 220 with Fowleri and maculiceps tangs, a pair of Genicanthus angels, a comet and a bunch of odds and ends. After the first week he developed a mild case of ich. I immediately began running my UV sterilizer and continued feeding heavy. I also had a pack of kick-ich and reef rally on hand just in case. It persisted on the tang for two weeks (without spreading to anyone else) before finally dropping off. He’s now a fat happy Achilles.