Well if you took out the carbon, you could cut down some foam to fit in the carbon's place.
I know you really want to, but honestly unless your kh is really low you don't need crushed coral. If you do decide to add it though, you'll need to put it in a filter bag (a mesh bag) first so it doesn't get loose and ruin your impeller.
I know you really want to, but honestly unless your kh is really low you don't need crushed coral. If you do decide to add it though, you'll need to put it in a filter bag (a mesh bag) first so it doesn't get loose and ruin your impeller.