Regarding the halimeda, I've had it in my tank for a little over a year with no problems so far...although I didn't find out about its ability to go sexual until a few weeks ago. Its fairly slow growing compared to caulerpa, but does take up a fair amount of calcium. As far as transplanting it into your fuge, just snap off a branch and stick it in the sand, or wedge it between a few chunks of rock and it will grow. I'd go more toward chaeto for the fuge though, I believe its much more efficient at sucking up nitrates than halimeda. Unless you just want something else cool in your fuge, in that case go for it.