I have a blackcap in my 75. I love him! As Dogstar said, he has done very well since he has been acclimated, but he was real skinny and had ich when I got him (I got him online).
He stays in the "depths" of the tank (they are deepwater fish). The only bad thing is I don't see him as much as the other fish because he stays in his cave alot. He isn't territorial that I've seen; in fact, the other fish chase him sometimes.