Mykayel may be right. But I would also wonder about your lights. What kind are they? My sump came with a 2 bulb NO light that the person before me said was growing algae great. But it wasn't working for me, it was dying off. I put some old PC's on it and now the algae grows pretty well.
That said, I could give you a handful if you want. It may have some grape caulerpa in it too if that's OK.