Generally there's no need for carbon except for removing meds ... experienced aquarists usually don't add carbon to their filters. Although I don't have a marineland pro series 280, in your case, I'd say let it be and eventually when the carbon's chemical filtration gets "used up" it becomes part of the biological filtration. See the link below for some more info on carbon filtration.
Activated Carbon In Aquarium | Aquariums Life
75g Planted Barbs Denison, BlackRuby, Tiger, Albino Tiger, Green Tiger, Cherry, Gold, Checkered, Odessa.
NonBarbs Cardinal, Neon, RummyNose, Bloodfin Tetras, Z. Danios. 1RTS. Amano, Bamboo, Ghost & RCS. 20g Long Shrimp Tank RCS, Tiger, Amano.