More nutrient export info:
http://www.wetwebmedia.com/nutrientcontrol.htm
Macroalgae
Macroalgae play an important role in closed marine systems. They utilize nutrients, such as nitrate and phosphate, which are found in abundance in most aquariums. As they grow, they take up required nutrients from the water column.
The use of macroalgae in marine aquariums is a matter of personal preference, but can provide the hobbyist with an affordable, natural means of exporting excess nutrients from the aquarium. Many hobbyists grow and harvest “purposeful” macroalgae, such as Chaetomorpha, Gracilaria, Halimeda, and Caulerpa somewhere in their systems in order to assist in the control and export of excess nutrients. By carefully cultivating and harvesting the macroalgae on a regular basis, you are literally removing excess nutrients from the aquarium. The macroalgae may be grown either in a separate section of a sump, algal turf scrubber, or even a refugium, depending upon the hobbyist’s preferences.
The degree of nutrient export provided by macroalgae is largely dependent upon the growth rate, density, and quantity of the macroalgae harvested. Under optimal conditions, some species of macroalgae can achieve tremendous growth rates, providing the hobbyist with a wonderful means to export nutrients from his or her system.