time for a science lesson!!! excerpts taken from
PH&G - Issue 18 - Nutrient Scrubbers Quote:
Algae, like other plants, must absorb nitrogen and other Nutrients into their body tissues for growth and reproduction. The development of the Algal Turf Scrubber simply simulates the processes that occur in nature on the weather side of coral reefs as the waves break against the reef and cross the reef top. In this area of turbulent mixing behind the breakers, a zone of short, dense, actively growing algae develops.
The underlying principle behind the growth of turf algae is the necessity for grazing by members of the animal population. The algae must be cut back or grazed, much like the grass in your backyard; or other species which are not as efficient at removing nutrients from the system will develop. And the need for nitrogen and other nutrients by algae is obtained from animal wastes, excreted into the water environment, a truly symbiotic relationship.
The Algal Turf Scrubber subsequently developed by the Townsville facility is a simple device that consists of a shallow tray with two removeable coarse mesh screens and a tip bucket at one end, which uses the fulcrum principle for tipping water across the screen. Aquarium water is delivered to the tip bucket, which tips several times per minute, causing a series of waves to rush across the screens. This water turbulence provides good mixing to facilitate gas exchange and nutrient uptake. Algae in the process of growing on these screens, takes up nutrients. Then, at regular intervals, the algae, with the incorporated nutrients, is scraped from the screens and discarded.
The performance of the Great Barrier Reef aquarium algal turf system has exceeded original expectations. This simple system is capable of maintaining low nutrient sea water, removing toxic metals, maintaining seawater pH and oxygen levels, together with possibly providing some degree of ultraviolet sterilisation.
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they use 1000 watt metal halides on their turf scrubbers, and use screen instead of roughed up plastic, and use crashing turbulent water instead of a steady flow of water. other than that, its the same basic system as the one we built.