Looks like cyano from what I can see from the pics on my phone. Being that your tank is 6 months old it's not the end of the world. I'd focus on water changes/nutrient export and possibly more flow as I've always seemed to get cyano the worse in areas of lower flow....
In the past when I've had to deal with cyano when I do water changes I suck up as much of the cyano as possible when taking out tank water. You may suck up some sand at the same time but if you hover over the cyano and lower slowely you'll get mainly the cyano with not too much sand...