You have left out some important info. Any fish yet, what are you feeding? Are you testing nitrates & phosphates with GOOD QUALITY tests? Yes, your tank is young and this is part of the process.
You probably have nutrients accumulating in the water column. This could be coming from fish & coral waste, residual die-off of whatever came with your live rock, leaching of stored phosphate inside the rock, over feeding, etc. Or any combination of these factors.
In theory the solution is simple - you need to export these nutrients down to a level where the algae is unable to grow and expand. But you need to test for these nutrients so you know where you are now and confirm that whatever exports methods you choose are indeed making a difference. It takes some time so be patient.
Proper & regular nutrient export will be the key. Your choices are many:
Water changes. Carbon dosing of vodka, bio pellets etc. GFO in a reactor. Siphon out detritus. Good skimming. Carbon usage. While employing these techniques it's important to physically remove all the algae you can.
All these topics are covered in depth in the stickies at the beginning of many different forums. Good luck.
