Hm. I couldn't tell you, absorbing nutrients from the water column and transferring them to the root system? Seems like another one of those 'miracle' aquarium products that don't work. I wish there were some reviews on the site.
I searched Google for other sites that sell it and none of the others have the 'remove nutrients from the pond water' quality listed. Except one, and that one looked kinda shady to me.