I believe most cardinals are most active in dim light, hence the large eyes. I had a trio i bought from saltwaterfish.com. (They carried them under the moniker "blue-eyed cardinals at that point.) Two didn't make it two weeks, but he third lived for about six more months and I beleive died due to crypt (marine ich). Mine was not as skittish as described above. He did live with a Banggai cardinal as well as several other generally non-aggressive fish. (Blue sided wrasse, foxface, midas blenny, royal gramma, ocellaris clowns.) They do get pretty big, and may pose a threat to shrimp, but mine was only about 2" when he passed. I have seen them closer to 3" at one shop once upon a time.