If the live rock has a lot of detrius on it at purchase you are best to "rinse" it off. just get a bucket of SW (natural or artificial doesnt matter, natural would prob be better as its free and you will basically dispose the water after, or you can strain it) and give it a shake, scrub before it goes in the tank. having it "clean" nakes it a lot better before putting in the display tank as it wont cloud the water. this does settle but it leaves crap all over the bed. rinsing and a gentle scrub wont hurt to much of the cultures etc. and it should build up life quite quickly.