Yeah, that's a good point - water does compact most grades of sand. But I wonder if fine to very fine gravel (particle size of 4 to 8 mm) might be an effective hydroponic medium. I think I may give it a try sometime, just to see.
Don't get me wrong, I still love my coco and always will. Not going to give up on that. I've just become really curious about whether sand or gravel could be an effective hydroponic medium, and now that the idea has taken root, I can't get it out of my head. I'm really curious to see how it would work. It seems to me it could be used much like hydroton - but being non-porous, it would basically be inert, and you'd have no problems with salt buildup or pests like fungus gnats.