That foliage rot in the pic isn't cause by the medium (rock wool). I get it on a few clones sometimes, the ones I leave in the dome for a bit after they've rooted, not all of them, maybe 1,2 or 3 out of over 100 usually will get it. I've also gotten it from unrooted cuts and rooted cuts sent in the mail. When the rooted cuts sent in the mail do it, they also always arrive too wet (saturated medium). Since they're mailed in a sealed container the foliage stays wet. How wet or moist does it stay under your dome? If you're getting water droplets on the leaves and domes I would suggest giving them some air frequently and wiping off the inside of the dome.