Hi there! One thing I notice is that your light looks very close for such young plants. The manufacturer recommends 24 inches above seedlings, and in my opinion that's still pretty close. I'd try to put it at 30 inches above them to start and I would guess they will perk up. When doing flood and drain with rockwool you either need to flood to the top of the block, or do a manual top feed to waste once a week. This is because salts will build up in the block at the flood line and need to be washed out once a week. Last year I did a flood and drain grow with 6 inch pargro rockwool cubes and even in flower I only flooded once a day. I think you need to let those cubes dry out more so that roots fill the blocks when dryback occurs. After the plants fully root into the cubes it will be harder to overwater them. Good luck!