Tom, phosban is just a brand of GFO media, which is used to lower phosphate levels in the tank. I would test your levels first before deciding if you need to run any.
The reactors themselves can be ussd to run GFO, carbon, or biopellets usually. Like mentioned, GFO removes phosphates, carbon removes some organics and toxins, and biopellets mostly remove nitrates but also some phosphates (though you'll need to run a skimmer with them to skim the effluent of the reactor to remove bacteria produced).
Again, I'd test your levels before you decide to run anything in the reactors and see if you even need to right now.