An algae scrubber has been discussed at length along time ago. It is basicily a shallow tray with a removable screen under the water level. Bright lights are used above it at a reverse daylight period,(i.e. light on at night when tank lights are off). One of the most difficult and important items was it needed a surge of water to make it really efficient which was also noisey. It would actually seed itself from the main display by just letting it run with the lights on. Micro and macro algae would start growing on the screen. Every week or two you would have to scrape the screen to export the algae. If you really want to get alot of info on it read the book "Dynamic Aquarium" by Dr. Adey. I bought it about 12 years ago. It is very in depth and describes the system at length. I belive it got a bad rap from alot of aquarium "experts" and was considered to be not viable. This so called expert are not heard of very often now. However Dr. Adey always stated that this was not a miracle solution to filtration but only one step. He patented the name "Algae Scrubber". Dr Adey's aquariums actually used alot of what is used today in modern reef systems. Deep sand beds, refugium, strong lighting w/correct spectrum, Aggressive and random water movement, and diverse lifeforms.
I consider him to have been in the forefront of modern reef technology but has was not given any credit for it.
