Dylan it has been reported to lower nitrate and phosphate levels in the Marine Aquarium. I'm not too sure if it has the same effect in freshwater. I used it in a heavily stocked tropheus display tank to achieve better water clarity. It does this well. It is also used to remove unwanted tannins which stain the fresh water, particularly when introducing previously unused bogwood etc.
Another plus is it is also easily regenerated using a 1:1 mix of bleach with water. Soak in this mix for 24 hours, drain, rinse thoroughly, and soak for 8 hours with prime or safe to remove the bleach from the product before reusing it in your fish tank.