First plant, deficiency question with details/images in post. 36 V

Hi everyone. I think i bleached my plant last week but i am not sure. Can you please help me identify the problem? Top leaves looks brighter/yellowish than others. Bottom leaves started slowly turning yellow and dying so i have cut them off. I'm feeding her with distilled water (PH 6.9) because i dont have a PH testing device yet. Last week i had them about 8 cm's away from my 250w MH and i might have caused bleaching or heat stress. I also suspect iron or magnesium deficiency. Thanks in advance!

 
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