You don't use bio balls in a fuge. The macro algae in a fuge produces the same result, without excess build up of detrius and garbage that gets stuck in the bio balls, resulting in them needing cleaned or they will no longer be effective and cause nitrate levels to rise.
Gravel is also not used in saltwater due to the same reason above. Crushed coral substrate also has this issue, which is why most people use sand.
Sand and LR
can be added to a fuge setup, but if the correct amounts are present in the DT then you are not going to see any other added benefit. I just have cheato in mine on a bare bottom.