leaves wont stop dying, pissing me off!

So,im a semi experienced grower. got two plants in my closet. a 2 foot cherry ak 47 and a 2 foot XJ 13. the cherry plant is tremendous, beautiful and healthy. no problems at all. but my xj 13 plant seems to not want to live. the bud structures seem to be forming fine. but all the leaves are dying. everything from browning on the side tips, curling down cupping in and turning brown and crispy. ive flushed the plant with filtered 7.5 ph water for a while now and am still not seeing any positive change. Ive had problems with it ever since i brought it home from the dispensary. so maybe its been fucked since jump street. hell i dont know.

information on the plants grow
water- 1 gallon of filtered 7.5 ph water

soil-earthgrow (ive used it for years and love it)

nutes- used a tomato food, but stopped because it seemed to strong even though i gave it a quarter dose.

temperature- 78 degrees

ventilation- good

lighting- one 48 inch dual tube flourescent light system hung about 1/2 foot fromt he plants. not too hot at all. and two soft white cfls in front.

please keep in mind that these two plants are in the exact same conditions. one is doing great and the other isnt. confusion is putting it lightly.
 
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