I just was suprised about the dramatic drop with just a fraction of GFO
It is very good at stripping PO4 and quickly. I added two tablespoons in a nylon stocking so it wasn't even tumbling on my tank with approx 45g and PO4 went from 0.4 to 0.0 in 2 days. For me works best when mixed with carbon in a reactor. Sure it doesn't work like as well as it could but IME it's works too well. Mixing it with the carbon seems to be a nice slow reduction not just bottoming out PO4