You might want to test your parameters. Can you give us readings?
Also, what kind of light do you use?
Furthermore, you can add iodine as a suppliment (Kent sells them). If you don't test for them, use sparingly.
Finally, use Purple Up because they have a balance of magnesium, iodine, and calcium when added. And boy, do they do a good job in my tank. The xenia's been in my tank for 3 months. I've given four stalks of them for credit at a local lfs
. And they did pretty well. I just tore them off the rock and rubberbanded them haphazzardly on a frag rock. they thrived.
Water and light is the key. Give some specs. Thanks.