The people I know who have been succussful growing succulents and caudiciforms with the clay balls do not use any other ingredients in the substrate. The balls wick and hold water quite well but there is an inherent limit in the packing efficiency so that there is always at least 25% (by volume) air in the medium, at last until the roots fill that space. The water-holding and air-holding capacity of the substrate sort of reach a balance.
