rock wool and fertilizers
You need to get as much of that rock wool off as possible. Use tweezers. It is saturated with fertilizers and is likely to lead to algae problems in the tank if you don't remove it.
Also, when you plant the plantlets, trim the roots if necessary to about 2 or 3 inches whatever looks right with the size of the plant, push it down in the gravel and then pull it back up so that the roots are showing just a tiy bit.