Brown spots / dying leaves

Hi ! I'm growing 12/12 from seed since nearly 3 months and my plant is showing real problems ...
I don't know the strain. Light is 125w ecolite. I can see brown spots on leaves and a lot of tips are becoming burnt/dark brown.
Is it a defficiency or an overfeeding? A month ago i think i've put too much fertilizer but i wonder why symptoms would appear only now ...

If someone could help it would be great thanks !
here is the pic

Nute burn ,reduce feeding.

ok thanks I hope it's not too late

omg even if i stopped feeding month ago, the leaves keep dying... they all turn brown and fall ... buds don't look damaged but will it survive with no big leaves ? thanks