The Algae Scrubber method
As opposed to a wet-dry filter Algal Turf Scrubbers grow ( turf ) algaes on screens that are in a seperate, but connected, system located outside or below the main aquarium. The basic concept is that the algaes remove nutrients from the water as their food source.
These screens should be scraped every 4-7 days as the algaes grow most rapidly when they are short. Harvesting the algaes regularly during their peak growth phase allows the nutrients, which are drawn up inside the algae, to be removed from the entire system.
The flow of the water across the screen(s) comes from the main tank and is returned to the tank That flow should be regulated, and if possible, alternated not just run from one end of the system to the other. This can be accomplished by a tilt tray or a dump bucket that creates a surge across the trays. The surge idea is to give the algae time to exchange gasses and absorb nutrients as well as provide light to all sides of the algae for maximum growth in a small area.
For these algaes to grow they need light. The lighting of an algae scrubber should be run the opposite to when the main tank lights are on. The reason for using a light cycle opposite from the main tank is to maintain stable pH, oxygen and carbon dioxide levels within in the system due to photosynthetic respiration. This prevents the wide range fluctuations found in most tanks. The type and output of the lighting will also affect the type of algae and growth rates. Nearly any type of intense light can be used, metal halide, VHO and HO flourescents, mercury vapor, halogen to name a few.
Within the tank, at the bottom, is a layer of sand or gravel approximately 1" deep. Placed upon the sand bottom is the live rock. The live rock forms the foundation that the living corals are placed upon.