We have had one for almost 2 years in a 200 gallon marine land deep dimension. 48x36x27.
Keys:
1. Get one from a healthy reputable dealer, like divers den.
2. Try to get a juvenile with the spot not fully developed. They adapt to captivity better.
3. Achilles exhibit ich like symptoms when stressed. I think too many people automatically assume it's ich and then start treating or quarantine and that actually is worse for the fish. It quickly goes away when they calm down. Obviously if it doesn't go away it's ich and you have issues.
4. Flow is huge for these fish. I have 4 mp40s. This fish is always playing in them. On full blast it will swim right up and put its nose right in the front, then spin and dart around the tank.
5. Swimming area - make sure you have plenty of swimming room for this fish. I have a 2 island structure with lots of open area for swimming and surging.
6. Live rock - I had very old established live rock from an experienced reef keeper when I started. My Achilles is always picking at the rocks. I also have a cave and arch structure, so lots of area for it to hide and play in and around.
I QT'd mine for 2 weeks in a 40 breeder. No lights other than ambient. PVC pipe to hide in. 2 koralia pumps, overkill for the QT, but this fish needs it's flow. Nori sheet every day, mysis and pellets. I actually would have put it straight in my DT if I wasn't QTing a Powder Blue that I wanted to introduce to DT at the same time.
Tank mates...a lot! Some of the heavy hitters:
Moorish Idol
Powder Blue
Chevron
2 yellow tangs
Regal angel
Several Wrasses
Copper Banded Butterfly
etc...
Mine eats pellets, mysis and Nori. Twice a day. Aggressive fish, but my powder blue is actually more aggressive. I had to get rid of a sailfin that was picking on it. All my tangs co-exist very well, but I planned for and introduced all at the same time so none would have territory established.
Good luck, great fish, fun to watch, very social. Will eat from my hand.