Clay pellets can be used as a growing medium for hydroponic growing. They don’t retain much water and cycle nutrients easily due to their round nature.
Other hydroponic growing mediums include Rockwool, Coconut fiber, Perlite and Vermiculite.
Learn about growing hydroponically in this article:
More grow medium definitions:
Grow medium | Soil | Seedling & Cutting soil | Hydroponic | Rockwool | Coconut fiber | Perlite | Vermiculite | Aeroponic