Seedlings problem

Has anyone had this problem before 2 week old seedling some of them are worse than others only 1 of 2 strains showing problem strain is sherbishna. 400 w mars hydro 24" above seedlings stays around 78 F and 50% H Grown in coco coir giving GH Flora serious and armor si, diomond nector, and rapid start at 1/4 strength for about a week and recently upped it slightly but tips are not burned just brown spots any suggestions would be appreciated.

Any calcium in there?

Thank you for response yes i am giving them full recommended seedlings dose of calmag and started calmag foiler spraying it seems to have slowed or stopped but just want to make sure its not something else