The light is 4' away? There are like 0 lumens getting to your plants with the light that far away. If you are still in the seedling cycle you need to use flouriecent lights. Switch to your MH once you have your 4th set of true leaves formed. No nutrients until then. Watch your Ph and don't over water them Rockwool can soak your plants so watch for overwatering.

Check your Ph and make sure it's 5.2 - 5.5 for Hydro.