I am really surprised that if the CC are poached out and there are BG left in there, that the BG haven't overpopulated. Are you absolutely sure there isn't something in there that is gorging themselves on the BG?

Probably a bad idea to just stock one LMB to grow big. It will just have a field day eating the fish you want to stock later. And like I said, maybe there is one in there already, or a large CC....