Seedlings need nothing, just water. You can just use RO water to be safe, pH about 6.3.
You will NOT speed things up with a feeding regiment on seedlings.
If you germinate a seed with maxi crop seaweed for 24 hr, It will grow faster, but never feed seedlings .... not even 1/2 strength, they just don't need it, it's like trying to feed a hamburger to a newborn.