I had problems with that exact algae for months:
It happened when there wasn't enough nutrient export for the size of my tank, and once it's established, I think it's better at capturing nutrients than something like a GFO or biopellet system was, so even though all my nutrient parameters read 0 or close to it, it kept growing.
I beat it by upping the flow through rate on my biopellet reactor, cutting back on feedings dramatically, a small army of mexican turbo snails (which mow through it like it's candy), and a two week course of AlgaeFix Marine by API, that you have to buy off eBay because you can't legally get it in Canada. After the Algae fix marine and snails had destroyed it, I stopped dosing the Algaefix, and it never came back. I can only assume that once it wasn't there to outcompete my biopellet reactor, the reactor took up the excess nutrients.