It's cyanobacteria. It's usually associated with low water flow or excessive nutrients. In a sump it's not so much of a problem unless it starts to smother your algae you are using for nutrient export. In a display it can quickly choke out and smother corals.
No that's cyano bacteria its kinda common to have in sumps because there's normaly not much flow in sumps.do you have any in your display?i would siphon it out and add some flow in that area