looks like some kind of green film algae, it's like the first green algae I remember seeing in my tank.
Strange that it's so low though, is the tank near a window or getting too much light? Do you use RODI water?
I remember I kept my lights off up until the very point of putting in my Coral to do my best to combat "The Dirty Stage" of the cycle. Do your weekly water changes, feed lightly once a day, feeding too much can leave excess nutrients in the water for the algae to feed on. Pulling uneaten food from the water column and filter will help. I have been doing this a while and I started to feed more because my Corals didn't like me taking out all the excess food I think. Wiping Algae out with an attachment to a siphon during water changes so it doesn't permeate throughout your tank could help.
Eventually you'll remove enough of it that it won't come back