halimeda for sure and it will just continue to grow if dont pull it out, had some in my tank about 12-18 months back, it doesnt really casue a problem unless you have some hard corals, even then I found it didnt have an effect on any of the prams in my tank but i did keep on top of it and ended up getting shot of the LR it had attached itself to as i was struggling woith bubble culerpa as well on the same bit