Prohibit outside views

How can the blogs be kept from other people seeing them. It would be great if only logged in users who have been accepted to the group could see the blog posts. For some reason when I first started it seemed like it worked like that? Anyhow, groups can be private and hidden, but I don’t see an option for blogs to do that? Really want that capability.

Thanks

http://ww.wp.xz.cn/plugins/bp-groupblog/