I have a display fuge off to side of my reef tank and a one spot that loves anything green. I doesn't matter if toxic for him or not, he still ttys everything. One macro that I have that seems to do the trick is C. brachypus. It is a nice low growing macro that makes a really nice mat on the substrate. One concern about caulerpa is when it goes sexual. This can devastate your aquarium but will rarely happen if you keep good parameters and trimming of your macros. Because its only a FOWLR, you could also try other caulerpas as long as your state allows them!