Bio balls are actually small multi-surfaced objects that provide massive "substrate" for the development of beneficial bacteria, usually run in a wet/dry filter. They were developed before the major change to reef aquarium keeping ... Live Rock and Live Sand, both of which you already have in your tank. Generally speaking I'd say you probably have enough Live Rock and Live Sand in your tank to forgo the use of bio-balls.
Just my .02 as usual.
Later,
Paul