I added a Entacmaea quadricolor to my 120 when it was 3 months old and I didn't have any issues. When I started the tank I used new salt water, new sand, and had 20% live rock the rest was dead. I took a lot of crap from 'more experienced' reefers, but I have no issues with the anemone other than it splitting and climbing all over my sps a couple of times before I got rid of it.
I recently setup a smaller tank using 100% live water from my 120, live rock and dead sand. I added an anemone after 2 weeks and it has been doing fine. I do spot feed every 3 weeks or so since it is 8" under a 130w PC fixture
That is my experience. I am sure that others will disagree, but it has worked for me and may or may not work for you. Good luck and let us know what you decide to do.