leaves are dying fast

ok so the bottom leaves are shrivelling up with yellow/brown spots all over them and working its way up the leaf sets of the plants. The plants also seem to be growing very slowly. Just today an entire second leaf set went from perfect green to yellow/brown and burnt looking. I just flushed them about 4 days ago and it didnt seem to help. So I sprayed some worm casting liquid onto the soil figuring it was some kind of nute difficiency, but that hasnt helped either. I think im screwed.

Im using schultz premium potting soil with 9 month slow release ferts (bad idea I know, but its too late now). They are in 1 gallon pots.

They were planted from seed about 5 weeks ago and are now only about a foot in height and are on their seventh leaf set.

they are sitting under a 600 watt hps with 18 hrs light.

i water them about every 4 days.

Any thoughts on whats going on here? Thanks:)

Sounds like you're killiing them will all the slow-release ferts.....that's just a guess because you could also have some ph issues going. I'd try and transplant them to a better soil asap.