Looks like cyanobacteria, but no need to "treat" it per se. There are recent threads lately about doing a blackout to kill it off and then vaccuuming it up. I had a small amount of it in my 29 gallon that went away when I adjusted my fetilizers. It will go away when lights, ferts, and co2 are in balance. Just curious how much lighting you currently have (wattage and kelvins).
Here's Haiwkin's thread about doing a blackout to treat his tank: http://www.tropicalfishkeeping.com/f...lackout-35508/
Also a recent thread mentions the use of Flourish Excel to control it (liquid carbon)
I love your tank setup...it looks gorgeous.