Is this green hair algae?

[habs247]

I'd like to nip the problem in the bud, if I can.

Doing some reading, looks like these are my options:
- reduce the photo period
- add a CUC or tang
- increase water changes (I did about 20% last week, planning same this week)
- manually vacuum it off

I think in most cases these are only ways to reduce the symptoms rather than fix the overall problem. I don't have a phosphate test kit yet, but I will be picking one up tomorrow (ammonia, nitrites, and nitrites all read 0). At any rate, I am using RO/DI water so I am confused with the source of the phosphate would be. I did start with mostly Marco rock, which I did not cook as I was under the assumption I did not have to.

Would appreciate your feedback, thanks in advance!