I would't put the seeds directly in the rockwool cubes to start with.
When you germinate your seeds, soak them overnight in a little bit of water in a small glass in a warm dark place. Initially, check them in a few hours and swirl the water in the glass to see if any of the seeds are saturated enough to sink to the bottom. Put the glass back in a warm, dark place. Don't worry if all or none of them sink right away.
The next day place a wet folded paper towel between two saucer plates with the top one inverted. Squeeze most of the water out of the paper towel. Place the seeds in between the paper towel, cover the bottom plate with the top plate turned upside down, place the covered plates in a large ziploc plastic bag, partially seal the bag and blow into the bag and seal it when you get a pillow effect. Put it in a dark, warm place and check it after 24 hours and then about every 12 hours thereafter.
Once the tap root sprouts, transplant it to rockwool that you have pre-soaked in a Ph'd water solution. You want the cubes to be moist, not wet.
Then set the rockwool into your net pots with clay pellets and setup your pump and drip system until the roots hit your res level and POW; they'll take off like there's no tomorrow.
Sorry if I provided too much info. I started with a very similar system 5 years ago and have learned a lot through trial and error, but a greater amount of information from the members here at RIU.
Good luck oin your grow. What strain you planning on growing?
