Chaeto algae (Chaetomorpha linum) is a hardy green algae commonly used in saltwater refugia & algae scrubbers. It is specially suited to algae reactors, where large masses can be kept with minimal packing due to its rigid structure.
It grows in long, curvy, sturdy strands that create a framework with ample inner space that provides shelter for a diversity of small, beneficial benthic creatures such as copepods, amphipods, isopods, etc. (it looks much like a green scouring pad!).
A fast grower when provided with bright full-spectrum lighting, this distinctive alga is valued by marine aquarists the world over for its ability to take up copious amounts of nutrients from the water column.
When the grow space has nearly filled, you can very easily harvest and discard a few chunks to complete the process of nutrient export. Because of its tough structure, it may be used in the main tank with fewer concerns that it will be consumed by herbivores.