Is this a deficiency or nute burn? :(

Thought I'd try out some auto flowering Big Buddha S.A.S. all was going well until last week. The leaves have started curling up.

Soil, Bio Bizz All Mix
Nutes: Bio Bizz Grow/Bloom, following the oldtimer1 feeding schedule
Lighting: 600w HPS in a cooltube
Airflow: passive intake, 120 Ruck extractor, -->carbon filter->cooltube->fan-->chimney
Temps: 67F(min)-85F(max)
Humidity: 35%-40%

BTW the soil isn't dry or compacted that's a top dressing of bat guano that I just applied

i tell you what my plants do this to me from time to time, i usually just check the ph and feed them with a complete fertilizer or flush. most people will say mag or nitrogen def.usually corrects itself from there. def start with finding the ph first

Soil ph is ok, it's currently 6.6, it's buffered by a dash of dolomite lime I use to keep the ph of the soil at around 6.5 as it can gradually creep up in flowering.

maybe a cal or mag thing.... either that or you burning her with that mix?...have you tried flushing and reading the ppms?

Is it creeping from the bottom to the top, leaves feel soft, turn whitish?