Seachem po4 remover, stocked by almost every LFS in CPT stocking marines. aluminium based bead shaped
Aqua medic antiphos, stocked by uncle Sam in Bergfliet and the shop in Plumstead. iron oxide based, crumbly granules
Liquid PO4 removal media stocked by Aquality, one of the sponsors.
There are no no studies I could find which proves which one is the most efficient at binding/removing/precipitating PO4.
They all work pretty well, only concern with the liquid is tht it may lead to a severe drop in alkalinity if overdosed.