GFO targets PO4, and may get some silica. Although you may get some impact on PO4 using carbon dosing, i.e. vodka, vinegar, BP's, etc. it is primarily used to reduce NO3.
I am looking to reduce phosphorus and nitrate. Considering adding a media reactor with gfo in addition to vinegar dosing. Sounds like they can coexist.
+1 those two products/philosophies tackle different problems. There is a hair of overlap but generally their primary functions are completely different. One aims to reduce nitrogenous compounds one will reduce phosphate