Ultraviolet radiation at a wavelength of 254 nanometers is extremely effective in halting the reproduction of algae. The algae readily absorbs the UV light which damages its DNA structure and makes it flocculate (clump together ) allowing it to be trapped in a mechanical filter.
Beadfilters are closed (pressure) vessels filled with millions of small plastic beads. These beads provide excellent mechanical filtration and enormous surface area for biological filtration.