In our very first tank, a 75g, many years ago, I made the mistake of putting some "lovely" grape caulerpa in various places in our mixed reef. Under MHs, the stuff grew like wild fire
Each week, I would pull out handfuls of the stuff, only for it to grow right back! One day, I decided I'd had enough. I pulled out each rock, one by one. With tweezers, a strong light to make sure I was getting it all, and a pail for dipping the rock in to keep it moist, I carefully picked the caulerpa out by the roots, some of which were deep in crevices. It took me two full days of going over each rock to get it all out. The extreme effort was worth it. It never grew back.
Good luck with yours
