It does look superficially like hair algae but it will siphon off very easily and if you try to grab it and pull it it will fall apart. If it was hair algae it would pull up the sand it's attached to when you try to do either. It's either dinos or cyano and all I would do is gently siphon off the top layer, rinse in fresh water, rinse again in H2O2 then rinse in fresh water again and let dry for a day or two before returning to the tank.
At 6 weeks old your tank is just beginning it's maturing process which can take 8-12 months. It looks to me like you just used dry rock and I'm guessing some bacteria. I'd suggest adding some quality maricultured live rock to introduce some of the microbial stuff that can't be stuck in a bottle and cryptic sponges essential for processing Dissolved Organic Carbon (DOC). See Aquabiomics article to learn more about how live rock helps mature a ssytem and here's links to some videos you may find informative:
Studying the effects of live rock in a newly established aquarium shows that high-quality live rock promotes the rapid establishment of an effective biological filter and a microbial community similar to those found in mature reef tanks.
www.reef2reef.com
"Coral Reefs in the Microbial Seas" by Forest Rohwer (Paper back is ~$20, Kindle is ~$10). Rohwer's book looks at the role DOC has in promoting coral diseases. This is a surprisingly readable book, sometimes funny, somtiems poignant, considering the complexity of the subject. His coauthor Merry Youle has also written a very good book on viruses "Thinking like a Phage" I'd reccommend also.
This video compliments Rohwer's book of the same title. While there is overlap bewteen his book and the video both have information not covered by the other and together give a broader view of the complex relationships found in reef ecosystems
Changing Seas - Mysterious Microbes
Nitrogen cycling in hte coral holobiont
BActeria and Sponges
Maintenance of Coral Reef Health (refferences at the end)
Optical Feedback Loop in Colorful Coral Bleaching
Richard Ross What's up with phosphate"