A great book on the technical aspects of the hobby:
The Reef Aquarium, Vol. 3: Science, Art, and Technology (Sprung, Delbeek)
http://www.amazon.com/Reef-Aquarium-.../dp/1883693144
It is a bit pricey but it is huge. The filtration chapter is 150 pages and covers skimmers, uv serilizers,refugiums, engs natural system, jaubert method, berlin method, deep sand bed, algal turf scrubbers and miracle mud.