I have added up to 8 pounds at one time without any bad effects. How it affects your system depends on a couple of things. How long has your tank been set up? Current bioload, and how cured is the live rock you are adding?
I'v added 30 pounds at one time before with out a hitch.I also added 5 corals and 4 fish in the same day.I know what most would say but never had a spike, a death or even a ich outbreak?????????