Has anyone ever looked into or tried to build a scrubber using "mirrored acrylic"? The link below goes to a UK site but I'm sure they sell it here in the states as well. Seems like it would be an excellent candidate for a material to box in a grow screen http://www.sheetplastics.co.uk/Acrylic_Mirror/3mm_Sliver_Acrylic_Mirror_Sheet
There were some threads discussing the use of this on the other site when the UAS came out, submerging this stuff may or may not be OK. For a waterfall unit, probably minimal benefit as it would only be used on the ends to reflect back lost light, but it would get reflected back to the other light fixture. Kind of falls into the "diminishing returns" category for me, but someone might find a way to put it to good use.
It might work well on single sided waterfall scrubbers where more light can penetrate through the back of the screen. Other than that though, I'm not sure there would be much benefit.
I use it on the ends of my box. Got it from Delvie's plastics. It looks like it's just regular acrylic with a metallic paint applied to one side. Figured it would give my scrubber a little extra oomph. No idea if it actually does anything or not.