Newbie Plant Problem

My first grow here are the details and problems. Any help/opinions/advice is greatly appreciated as I've learned alot through the community
1. Age is almost 7 weeks.
2. Strain is White Label Northern Lights Fem. 3. Grow is in rockwool.
4. Temps are are between 78-82 degreesF.
5. The light is a 400w mh (plant is 3 1/2 ft away from the light).
6. Stems are purple.
7. PH is between 5.5-5.8
8. Nutes are David's Grow.
Plant problems are
1. Leaves dry up, curl upwards, turn brown and die.
2. New growth continues but all the bottom leaves have fallen off and dies.
Attached are some pics please let me know what additional info you need.

try less nutes

I wish I could get a little more help/advice. I'm sure more people have a quick opinion on my plant problems. Please Help...

is this a ebb & flow? You have no details on what type of grow this is. If that is 7 weeks i would try again. Throw it into flower if you want. Maybe your roots are lacking oxygen. Over did the nutes? how often are you feeding and do you check the ph after you mix nutes of before? Whats the ppm of the nutes? I would have to say its a root problem if that is 7 weeks, the growth is stunted.

Yes its ebb and flow and I may have overdid the nutes as I couldn't measure the ppm. If I took what clones I could from this plant could I start over from there? Or would the roots from the clones be bad as well? Should I start from seed again?

I'd start over....those pics look like goners to me...try putting them in soil and see if they snap out of it?