i'll try to answer, i empty the second tank meanwhile ^^
A. i pre soak the block for a week/10 days to get a stable pH at 5.5 ( and the last day with a 0.8EC solution to add some nutes in the block )
B . i don't have lot of root, but the yellow leaf on the bottom was turning left a few days ago, i though it was because it was the first leaf (the part i cut from the mother plant)
you may have right for the small one who has a yellow leaf on the top, i think he don't have enough root.
like 1