problem with leafs

hey these are my plants after 1month in my grow tent 120x120cm and 400w metal halid light. Iḿ just experiencing some problems with leafs. They seem to be burnt or maybe got a mold. Can anybody give me any advice what might I be doing wrong? also I think that they are too low for 1month old plants arent they? thx

Do you let the soil dry between feeding/watering? The leaves look like they are saturated with moisture giving it that spinach look at the tips. Might be overwatering. Not sure though.....