One of the trickiest things about hydro is starting sprouts. They'll stall, won't grow, and looks like it's drowning. When I did hydro, the sprouts were grown in grodan cubes until it had enough roots coming out of the cube to survive living in water. (Seedling)
Some members here will grow the sprout in soil until it's a strong seedling. The dirt is washed off the roots and then it's put in the machine.
My advice is experiment with both methods. The sprout pictured is sickly and it'll be a fight to get it to take off. It needs to be bigger/stronger before putting in hydro.
Be warned. You're gonna kill lots of plants until the process clicks and you get the method down.