I am going to get some LECA (Lightweight Expanded Clay Aggregate LECA (Lightweight Expanded Clay Aggregate) (Fired Clay Pebble) Hydroponic Media Products at Home Harvest® Garden Supply) that was suggested in another post. The one problem I could see with this is that the stones seem to be 8mm-16mm (.31 inches - .63 inches) in diameter and therefore the substrate could wash out past the stones. What would you suggest for this? Will it be a problem?