Is it a 400 or a 1K MH? I have put seedlings under a 400 MH with no problems, just give it more space than usual from light to canopy. Normally my 400 can be anywhere from 8"-12" from the canopy, but when I do seedlings under them, it's more like 2' away. If it is a 1000, i'm sure the same principle would apply, but I have never done it so I can't necessarily recommend it.