Could be cyano but its hard to tell from the pics. Get a closer pic and does it easily blow off tbe rock? Cyano is not something to fear as it is easy to deal with and normally with natural methods. Micro Bacter Clean, Vibrant, Dr Tims Waste Away and Live Rock Enhance are all effect natural methods to removing cyano. Proper nutrient levels, good flow and well rounded clean up crew help reduce and prevent blooms.