These fish are one of the harder tangs to keep and they generally do better as the only tang in the tank as they will stress if they have to do battle with other fish. Stress is a major factor in the demise of captive achilles, they will also do better if they are the alpha fish in the system. A tang like a yellow that is a different color and shape is better than some tangs like a powder blue or other species that share the achilles shape but having the achilles as the only tang in the systen is best bet. They like a big tank, excellent water quality, and lots of water flow. I have kept this fish twice, both times for over two years. The first died when I had to tear down and move the tank, the second was eventually killed by my asfur angel who would kill any aggressive tangs but interestingly enough left other mellow tangs completely alone.