5 easy ryder seedlings died --help

i tested the water ph - it was ok. when I put the seedlings in rockwool plugs under the dome - they looked fine. 400 watt MH 3 1/2 feet away - temp was 85 w/30% humidity. I watered them daily but if the rockwool felt damp, I would water them a little --few dayslater they just fell over and died --please advise -- the seeds cost $11 each!!

Kinda hard to tell if we don't really have pics. But i'll tell you that a MH can do serious damage to seedling sometimes. Your safest bet is to start out with CFL's and build their strength up. Also if the rockwool is even damp you don't need water. Its a weed not a whale. They don't always need water. Too much water will rot your roots out.