Drop your pH to 5.6-5.8 range.
There are a lot of things that determine the rate of transpiration in a plant...in some of the specimens you have showed us it is clear that the rate of transpiration was too slow to keep the entire leaf moist. Moving air can cause the edge of your leaves to go dry, also if your newly developed root systems are being damaged by air and light it can reduce your specimen's ability to provide water to the entire plant structure. you may have a mold problem, a pest larva problem or all of the above, it's really hard to know.
Your challenge is to increase the rate of transpiration without over watering the plant. Remember rate of transpiration is directly linked to rate of evaporation at the surface of the leaf. I would try putting covers over the pots to start, limiting light exposure and aeration of the roots. It might be necessary to increase your watering cycle depending upon what temps and humidity levels exists in your grow space.