How much do you use ? Because the first thing your going to here about is that rockwool sucks and should never be use for anything. I have seen coco peat mat but not heard anything about it or soilless mixes. Peat holds too much water and the others won't hold up plants. If you can't get hydrotron clay then use lava rocks for gas grills and break it up to the size you want. It's cheap.