Fuk rockwool i hate that stuff & have zero luck with it , i grow flood n drain using clones grown in root riot sponge cubes vs rockwool , you can plant seeds directly into root riot sponge cubes,wet the cubes one time then put them into a sealed humidome someplace warm, just look at the cubes once a day & its easy to see with the naked eye weather the sponge cubes are still moist or not , just keep the cubes moist with a spray bottle & in the humidome & your all set .
Leave the sprouted seedlings in the humidome & keep moist until roots are sticking out a few inches from the sponge cubes then put the sponge into net pots & fill the pot with hydroton or your medium of choice & your ready to go , ive had excellent & reliable results using Root Riot sponge cubes & being the cubes are less than an inch round its nearly impossible to over water .