It doesn't look like cyano to me, but more like hair algea. If it is cyano you should be able to blow it off the rock. Be careful with doing this because it will spread. Hair algea will take a small amount of force to remove from the rock.
Nevertheless looks like it's just part of your cycle.
I never figured mine out but looks exactly the same but mine is pretty much limited the back glass. Have a beefed up CUC coming Wednesday two of my astraeas committed suicide and fell off the glass landed on their shells and I didn’t see them for 24 hours. Oh well time will tell one astraea is working away but need help lol