at 6 weeks in diatoms (gold/brown dusty looking stuff) are to be expected and not really a cause for major concern. They will die out on their own as they utilize the free silica in the water. It's often more of a pain in the butt to try and control them rather then just letting it run it's course.
Also flow has little impact on diatoms, but UV sterilization does help a bit.
It does look like the starting of some cyano on the top of rocks, the pink/reddish patches.
Is their livestock in the tank currently?
What/how much are you feeding?
getting cyano 6 weeks into a new setup isn't good, it indicates that there are too many nutrients in the water column, and you shouldn't have that issue so early unless a lot of organic matter/food has been put into the tank.
Is this a tank that was moved/reset-up or something? I notice spots of coralline on the walls. If you used materials from another setup, was the rock/sand clean?
Just trying to understand why you have cyano starting so soon.
Overall though, relax, you've got at least another 6 months to go before everything really settles down and achieves a good equilibrium.
