The Powder blue and achilles are very similar shape. I think you are going to have a problem if you try to introduce an achilles. Plus they are not an easy fish to keep to begin with.
i kno i'm thinking now it'll probably be impossible to find an achilles in a week. that would be the longest i could wait to add another one. i also think that because their bodies are all the same they might be aggressive toward each other. so i would like to find a chevron tang. what are the thoughts on that?