Stumbled upon this
"An improved algae scrubber system having a partially submerged rotatable drum wrapped in plastic mesh or algae screen"
http://www.google.com/patents?id=EUI...ed=0CDMQ6AEwAA
Seen this idea floated on here a couple of times and I did consider building one myself to try it out.
Interestingly the patent was filed ten years ago.