From the photos that is probably not algae. It is probably either dinos or cyano. They can look very similar but have different causes. Does it tend to mostly go away after the lights are out and then come back after lights on and get more pronounced as the day goes on? If so one of the things you can do right away, whichever it is, is to suspend some floss near the waters surface. You can use something like a nori clip and tear off a piece of filter floss and clip it. Use a cheap floss as it is best to use a new piece each night. What will happen is that when cyano/dinos go mobile at night, some of it will get trapped in the floss. Throw the floss away when the lights come on or even a little before they come on.
Further remedies depend on which it is. Cyano is bacterial and dinos are one of several strains of a dinoflagellate. The best way to get at least a reasonable guess as to which is to test the phosphates and nitrates. If they are kind of high it is probably cyano and if one or both of the parameters are zero then it is probably dinos. If I had to guess, I'd guess cyano just because it is a little more likely in a young tank that doesn't have a lot of expensive filtration equipment. But, as Tim mentioned, dinos are almost as likely because fresh rock and sand can act like a nutrient sink. Test Nitrate and Phosphate and we can give you more recommendations.
