why would you not want to use rockwool in a hydro system that uses a pump? Hydroton may not be easy to get completely clean initially. But reusing it is easy. I just soak mine in a ph'd water/mild bleach solution overnight and they are perfect. Hydroton and rockwool are the most popular mediums for hydroponics for good reason.I would not use rock-wool with a hydro that has a pump. The combination of rock-wool and pump is very bad. I think I would use rapid rooters or preferably Sure to grow media. Don't take a chance with other medias causing your system to fail when you're not around. (SAD, SAD, SAD) Actually hydronton is not on my favorite list either. You can't get that stuff clean enough.