Naww don't get cartridges, those will have carbon. Sponge, filter floss, bio balls and ceramic beads are all nice, not sure how much room you have in there.
Parking in my town.
Thinking to buy a 10 gallon and try the whole fiddler/hermit/red clawed crabs thing.. You know, instead of more bettas. After the 90 gallon, it'll just be goldies and the cichilds for a while, can't decide what else I want.