They do not need a big tank at all, depending on their size. If it is a small one a 10 gallon would do. They do need hiding spaces, though. You are correct that they need to be kept alone. Be careful because they can split you finger if you are not careful. I had a few in my reef tank that I finally got out after 6 months. Just be sure you want one because I don't think anyone will want to take one back!!!