Chaetomorpha, also known as Brillo Pad Algae

[Delphinus]

I could be wrong on this, but I think it grows better as a free floating tumbling mass, so in a sump, refugium or aquaclear kind of thing might work better than just in the tank. You could probably stuff some under a rock to hold it in place but I'm not sure how well that will work long term, it will probably eventually get sucked into a powerhead input or some such.