Croceas are probably the most 'finicky' clam in my experience with Maximas , Derasas and Squamosa being more forgiving. I have a derasa I got from a group order here several years ago at about 4 inches that is almost a foot across! Plan accordingly - croceas are nice in that they are small - I would reccomend keeping it high in the tank on the rockwork as they tend to bore into coral rock in their natural environment.