Looks familiar. It's probably a combination of pH and the MG being too hot for the seedling. In the past, I had to take them out of the pre-fertilized soil and put them in some seedling starter mix. I'm not exactly sure what your next course of action should be... they can pull through, but like I said, in my case I had to do some careful careful transplanting. Prior to that, I just sat there and watched them do absolutely nothing while they stood there in shock.
The first set of leaves, Cotyledons, will usually fall off. They are mostly for that first growth spurt. No biggie.
Cannabis does like a wet/dry cycle... but the time of those periods will vary depending on strain/conditions. You don't really want it to get completely BONE dry... but you want to notice the weight difference between that, and a freshly watered pot. Once you pick it up and go "Woah, that's light" it's time to water
Oh, and I wouldn't really expect any damaged foliage to gain its old luster back. To get an idea as to how the plant is doing currently... focus on the top 1/3 of the plant. Damaged leaves will usually either stay the same... get worse... or just fall off. As long as the plant is growing up and out... you're doing at least 1 thing right
