calcium magnesium deficiency probably. ive had this a few times, the lower fan leaves would start to roll and collapse and get crispy. the necrotic spots also.i just hit it with some cal-mag and it cleared up. when i used the mgsoil (budget issues back in the day) it was usually pretty heavy on some things and lacking in a lot of others. i would pick up a bottle of some type of bloom enhancer thats low in nitrogen but has more phos and potassium in it. for instance the npk ratio might appear as 0-10-10 .if you dont have access to a hydro store,you might be able to find something like cactus juice /earth juice or a liquid bloom at your local market/nursery. the warmer temps might aggravate this condition but the plant can make it thru. ive flowered at 90 using similar strains with minimal damage but the stretch was a mofo.