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.