Bio Balls Are Used To Provide Increased Surface Area For Benefical Bacteria To Grow On In Your Pond Filteraton System..Bio Balls Have A Larger Surfurce Area Per Cubic Foot Compared To Lave Rocks. The Biological Filter Is A Very Important Piece Of Your Pond Fitration System..Replacing The Lava Rock In Your Biofalls Filterwith Bio Balls Will Increase The Biological Filters Capacity,Improving Yourfilter System.