Just because its white doesn't mean it's dead. I've had my share of algae, and this was one of them. It actually grows white, as long strings, sparsely branched. Don't assume that it died off, because it will keep growing. Mine even grows on my snails. I don't have a way to get rid of it, but my tank seems to be past it. In fast, I lost MOST algae when I started fertilizing more - N, P, K and traces. If you're not fertilizing, you should look into it. If you are, you may want to increase some levels, depending on what you're dosing already.