I pulled all the rock from my 30g, at least 30 lbs; it was covered in bubble algae I just could not win the battle. I replaced it all at once with life rock and had no problems. I did have additional biological filtration with seachem matrix in my back chambers. It was completely filled with mostly lps; chalices, euphylias, and even a derasa clam, a 2 dwarf lionfish.
I also added a 40 lb box to a 90g when I did a transfer and had no issue.