Ok I have a 75 gallon set up with 40 lbs of live rock and a Rena XP4 packed with ceramic rings. I wanted to add about 30 lbs more of live rock. Can I just add the rock at once???
if not then go for it! it may cause a mini-cycle but if you dont have any stock i wouldnt worry about it. If you purchase curred rock from your LFS then you probably wont even see any parameter changes anyways but it depends on how much you let the rock dry and how curred it was before purchase
if you've got fish in the tank then i'd only add the rock a bit at a time(like 5~8lbs every week) so that you've got enough of a bio-filter to remove the extra ammonia before it has any time to damage anything.