Starting last night my plant was in total darkness. Thanks to you guys i think some white hairs are coming out, thought im not sure yet.

But im having another problem now some leaves sre turning brown so :

Light 400W HPS 15 inches far from the top leaves
Watering every 3 days 1.5 Liters ph 7.21 ( because of nutes making the soil more acidic )
Nutes every 3 waterings NPK : 8-8-8
Fan blowing 12 hours in light cycle

What can it be ???

Sorry for all the questions i tried to find what is wrong but i couldnt find exactly whats wrong.

Thanks alot