This is Feather Caulerpa - it grows runners, puts down roots, and is recognized by these "leaves" standing straight up. It can be a pretty display for a Seahorse tank, perhaps. Not the best choice for nitrate absorbtion. It will grow nicely and isn't as prone to "going sexual" as other Caulerpa species. I wouldn't recommend putting this in the display tank, nor would I feed fish in the display this macroalgae since undigested matter could take root in the rockwork.