Leaves are gray/brown and curl down. HELP!

Hey, i'm also a first time grower and went through something similar (you can check my question). I could not exactily figure out what happened, but i think in my case the probable cause was either overfeeding (started fertilizing too early) or the leaves touching the wet ground when wilting. I am also using biobizz, but am growing in lightmix so i don't really know about nutrient concentrations in your case, still ,i'd say its either overfeeding causing a nutrient lockout or underfeeding. I'd skip the fertilizer for the next couple of waterings and monitor the situation (better to underfeed than to overfeed). Also, just to be sure, try to find something to hold up the leaves and see if it stops.

I think it's too wet because the old leaves are affected. Too many nutrients would affect the youngest leaves. I wouldn't water for the next couple of days! Just a tip... If you're not sure if you should water because it might be still little bit wet, just water on the next day. Cannabis likes it rather dry than wet. And always lift your pot a little bit and check the weight before watering to see how wet the soil is. Good luck buddy ✌️