I just cycled my 55g with all BRD dead rock. here is what I did:
~~Temp 79, no lights, no water changes until finish, skimmer on
Day 1, filled with water
Day 3, Got some sand from tanks at , CF, TRS, ABC, and a member's tank and put it in a plastic container in my sump
Day 6, added a cocktail shrimp to the sump in a stocking on a string
Day 8 took shrimp out because it smelled so bad
from this point on i added about 1/2 lb of cycled liverock rubble and kinda destributed throughout the tank to speed up the process. Got the rock from TRS ( cost me like $3) and i got small clean pieces to avoid hitchhikers.
Day 9, Started testing, and noticed ammonia spike also went to PetCo and purchased bacteria culture Just for a good measure. Added a pinch of food pellets to the tank to get enough decay.
Day 16, Ammonia was gone and Nitrites were sky high
Day 25, all was leveled and Nitrates were about 10-15 so I did a massive 30% water change
Day 26, tossed some pellets in to test for ammonia spike
Day 27 measured for ammonia, and nitrites and there were none
Day 30 started adding cleanup crew and other lifestock, no sign of diatoms or algae, lights went on.
started adding lifestock after that, everything is stable, about 4 days ago I finally got a diatom bloom and it was gone in 4 days and now hair algae is showing up in some spots ( part of normal cycle).
hope this helps cause i searched everytwhere for a guide like this wen I did it
Edit- Kat, to answer your question, the more LR you get the faster the cycle would be, I did 1/2 lb per 50+lb i have in there, and I bet if you add 10lb to your 120 you'll cycle in 3 weeks or so.