turf scrubber, not working (at least nothing growing in 8 weeks)

[Jaws]

I'd recommend having the water fall directly down over the mesh. Flow's pretty important for both sides of the screen so the algae can attach and grow. And a sander might not be the best tool for roughing up the screen either. Lots of deep and wiry cuts will help the algae flourish as well. I cleaned my screen once a week for the first couple months too to promote growth.

[Money pit]

There's a couple things you can do to fix it
First you need your reds to be in the 660nm range, Cree are in the 630 range I believe
Second, its hard to tell,but I think Jaws is right about the screen needing to be roughed up some more. The holes in the pic still look square, they should be almost filled in with the little pieces.
Also I didn't see if you mentioned flow, but its 35gph per inch of screen across the top.
I just took another look, and realized your screen is narrow across the top, and long up and down. Typically they are long across the top and shorter or the same size up and down. I don't know why, but I seem to remember back when I was reading up on these before I built one, that this was important. Sorry for being vague one this point, but I can't remember the details.

660nm led
http://shop.stevesleds.com/Philips-L...S-Deep-Red.htm
http://www.ledgroupbuy.com/deep-red-660nm/