I would not try Lava rock. It breaks down over time releasing toxic levels of sulfur and other unwanted minerals into the solution. They are also not ph stable. how coarse is the sand. If it has been used you are going to need to sterilize it. Sand work ok for a variety of different crops and I am sure it could work just fine you may just have to fine tune the watering, sand holds a ton of water. search online for more info on hydro using sand for more tips and info. Do not use bark, breaks down to fast, and coco work great, depending of the system used. Good Luck.