Yellowing leafs and brown spots

Hello everybody. First i would like to sorry if there will be any language mistakes as english is not my native language. I have some problems with my Pineapple Chunk girl which are visible on photos i put here(sorry for poor quality but i only have phone camera). She is auto and feminised, pot is 18 litres, soil was bought in shop, its "canna light mix" mixed with normal soil (also from shop) and dolomite. lightning is 400 wat HPS. Girl lives in room without good ventilation so i putted 2 standing fans in there but still its really hot in there, about 35-40 C degrees (i know its way too high but i cant do anything including moving her from there). I didnt use any fertilizers untill she was 3 weeks old, then i used biological fert (im sure that problem cant be caused by it as it started before using fert). I use water from sink which i leave for a day or two before watering, to remove chlorine. Now she is about 50 days old and still on veg. I think its enough info about grow so now i'll write smth more about problem. Lower leafs started to look like those on photos, brown spots and yellowing leafs, then leaf dies. I posted similar topic on my native canna growers website but they arent really helpfull and keep saying that its 100% healthy plant....
I beg you good people, help me and my lil girl and im sure that Jah will bless your souls and plants ofc ;) Best regards.

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