I've lost at least half or more of my seedlings that I started on January 4th. (about 20+) Including 5 of my 6 Fataliis. All were started in rockwool and then transplanted up into cups with Pro-Mix BX. I placed the whole cube in just below the soil surface to cure some legginess. They were light starved in the beginning, but then got switched to a south facing window and eventually a mini greenhouse in the window. I thought I was watering them enough as the soil always felt moist and the air was cool and I wasn't getting much evaporation. What I have eventually discovered is that although the soil was moist, the rockwool cube inside it was bone dry. My roots had never made it out of the rockwool and the plant died from lack of water. I think the Pro-Mix had a greater affinity for water and just sucked the cube dry. I subsequently have watered just the cube under the soil of a few plants showing the same symptoms and they immediately recovered. Just thought I would share this info with anyone else using rockwool and water attracting soil. I've always tried to be careful not to over water and instead was doing the opposite. I kept blaming it on lack of light, low temps, wrong nutes, lack of nutes, etc - but it was just simple - no water to the root. Lesson learned.