For starters, you don't need a dripper system with a Deep Water Culture.
Your rockwool is too high, you should have it below the pellets.
Make sure there are enough roots at the bottom of the rockwoll cube.
Place a couple of layers of pellets in the arse of your net pot, then put the rockwool cube on top of those layers and cover around and on top with more pellets. A layer of fungus will grow on top of your rockwool if light gets at damp rockwool.
Hand water around the rockwool (just the pellets) for a couple of days, the roots will make it to the water by itself. Keep the water level below the bottom of the net pot. The fizzing from the water will splash up to the net pot to keep the bottom layer of hydroton damp.
Remember a pump running constantly in a batch of nutes will raise its temperature