Yes it is Blue Green Algae.
This is not a true algae, but a bacteria called Cyanobacteria.
Even if you decrease the photo period and use combative methods used to get rid of traditional algae, it most likely will not work. You most likely have this stuff because of excess nutrients. I had a ton of this stuff in my tank and it spreads like a wildfire. You can spot treat it with a syringe full of hydrogen peroxide. This will almost instantly kill it temporarily maybe permanently, but I would not count on it to disappear forever using hydrogen peroxide.
Just do some research about it on google.
BTW, high concentrations of hydrogen peroxide can and will kill your fish and maybe your aquatic plants so be careful. I used about 1ml or less per gallon of water.
Do some more research on hydrogen peroxide on this forum or google.