Hydrokorrels Clay is the best there is. It is clean, pH neutral, pH stable and is used in hydroponic and aeroponic systems. Hydrokorrels Clay is also a useful additive to Coco Medium and Soil when growing in Pot Culture and also anywhere where extra drainage is needed. It is possible to re-use Clay Pebbles once or twice maximum by cleaning them through with liquid oxygen.
N.B.: We do not recommend that you re-use clay pebbles more than 2 times as you will definitely notice a drop in yield if you do.