If you want to run media like carbon, GFO, or bio pellet media but don’t have a media reactor, you can run these in canister filters. The canister filter, though typically viewed as a piece of equipment better suited for freshwater and used by newbie saltwater aquarium hobbyists, is actually quite versatile. You can use them to polish your water with fine filter pads and carbon, or you can use them to run bio pellet media and even GFO. Granted, you won’t be able to see the media in the chamber as you could with a media reactor, but in a bind the canister filter will work wonderfully. If you want to run GFO media to decrease phosphate concentrations, I would suggest putting it in a fine mesh bag prior to running in the canister filter, otherwise you might get some of the rust colored media in your aquarium.